13.68: Pregnancy and Childbirth - Biology

13.68: Pregnancy and Childbirth - Biology

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Why is it called labor?

So…the mother carries the developing baby for nine months. We know about the tremendous growth and development of the embryo and fetus. Then comes labor.

Pregnancy and Childbirth

Pregnancy is the carrying of one or more offspring from fertilization until birth. It is the development of an embryo and fetus from the expectant mother’s point of view.

The Mother’s Role

The pregnant mother plays a critical role in the development of the embryo and fetus. She must avoid toxic substances such as alcohol, which can damage the developing offspring. She must also provide all the nutrients and other substances needed for normal growth and development. Most nutrients are needed in greater amounts by a pregnant woman, but some are especially important, including folic acid (vitamin B9), calcium, iron, and omega-3 fatty acids.


Near the time of birth, the amniotic sac breaks in a gush of fluid. Often when this occurs, women say that their "water broke." Labor usually begins within a day of this event. Labor involves contractions of the muscular walls of the uterus, which cause the cervix to dilate. With the mother’s help, the contractions eventually push the fetus out of the uterus and through the vagina. Within seconds of birth, the umbilical cord is cut. Without this connection to the placenta, the baby cannot exchange gases, so carbon dioxide quickly builds up in the baby’s blood. This stimulates the brain to trigger breathing, and the newborn takes its first breath.

Immediately after birth.


  • A pregnant woman should avoid toxins and take in adequate nutrients for normal fetal growth and development.
  • During childbirth, contractions of the uterus push the child out of the body.


  1. What causes the fetus to be pushed out of the uterus during birth?
  2. Why is the umbilical cord cut before a newborn has started to breathe on its own?

Experiences with Achieving Pregnancy and Giving Birth Among Transgender Men: A Narrative Literature Review

Despite the burgeoning scholarship on transgender health and health care, the literature on transgender reproduction and reproductive medicine remains limited. In this narrative literature review, we examine recently published studies focused on the pregnancy and birth experiences of transgender men to provide an overview of the literature's major contributions and illuminate the gaps that exist within this research. Our review reveals that transgender men face substantial obstacles to achieving pregnancy and significant challenges during pregnancy and birth, which are informed by institutionalized cisnormativity embedded within medical norms and practices. This article demonstrates the importance of better understanding transgender men's reproductive health care needs in order to improve the quality of pregnancy-related health care delivery to this population. Our findings also provide insight for researchers, health care providers, and educators seeking to create and enhance gender-affirming medical education and training.

Keywords: childbirth health care delivery pregnancy reproduction transgender health.

The real reasons why childbirth is so painful and dangerous

Giving birth can be a long and painful process. It can also be deadly. The World Health Organization estimates that about 830 women die every day because of complications during pregnancy and childbirth &ndash and that statistic is actually a 44% reduction on the 1990 level.

"The figures are just horrifying," says Jonathan Wells, who studies childhood nutrition at University College London in the UK. "It's extremely rare for mammalian mothers to pay such a high price for offspring production."

So why exactly is childbirth so risky for humans? And is there anything we can do to further reduce those death rates?

Scientists first began thinking about the problem of human childbirth in the middle of the 20th Century. They soon came up with an idea that seemed to explain what was going on. The trouble began, they said, with the earliest members of our evolutionary lineage &ndash the hominins.

From an early date in our prehistory, hominin babies may have had to twist and turn to pass through the birth canal

The oldest hominin fossils so far found date back about seven million years. They belong to animals that shared very few of our features, except perhaps one: some researchers think that, even at this early stage, hominins were walking upright on two legs.

To walk on two legs efficiently, the hominin skeleton had to be pushed and pulled into a new configuration, and that affected the pelvis.

In most primates the birth canal in the pelvis is relatively straight. In hominins, it soon began to look very different. Hips became relatively narrow and the birth canal became distorted &ndash a cylinder that varied in size and shape along its length.

So from an early date in our prehistory, hominin babies may have had to twist and turn to pass through the birth canal. This would have made birth a far more difficult task than it had been previously.

Then things got even worse.

About two million years ago, our hominin ancestors began to change again. They lost their more ape-like features such as a relatively short body, long arms and small brain. Instead they began to gain more human-like ones, like taller bodies, shorter arms and bigger brains.

That last trait in particular was bad news for female hominins.

I was going to find evidence that supported the obstetric dilemma, but very soon everything came crashing down

Big-brained adults start out life as big-brained babies, so evolution came into conflict with itself. On the one hand, female hominins had to maintain a narrow pelvis with a constricted birth canal in order to walk efficiently on two legs. But at the same time the foetuses they carried were evolving to have larger heads, which were a tighter and tighter fit through those narrow pelvises.

Childbirth became a distressingly painful and potentially lethal business, and it remains so to this day.

In 1960, an anthropologist called Sherwood Washburn gave this idea a name: the obstetrical dilemma. It is now often called the "obstetric dilemma". Scientists thought it explained the problem of human childbirth perfectly. Many still think it does.

But some, including Wells, are no longer happy with this standard explanation. In the last five years, Wells and several other researchers have begun to push against the classic story of the obstetric dilemma.

They think Washburn's idea is too simplistic, and that all sorts of other factors also contribute to the problem of childbirth.

Holly Dunsworth of the University of Rhode Island, Kingston, was drawn to the obstetric dilemma while she was still a grad student. "I thought it was so exciting, I was going to find evidence that supported the obstetric dilemma," she says. "But very soon everything came crashing down."

We have bigger babies and longer pregnancies than you would expect

The problem was with the predictions Washburn made. "When Washburn wrote his article, he was actually saying that the obstetric dilemma was solved by giving birth to babies at a relatively early stage in their development," says Wells.

Go back to that moment two million years ago when human brains began to grow larger. Washburn suggested that humans found a solution of sorts: shortening the length of the human pregnancy. Human babies were forced out into the world earlier than they really should be, so that they were still relatively small, with diminutive, underdeveloped brains.

Washburn's explanation seems logical. Anyone who has held a newborn can appreciate how underdeveloped and vulnerable they are. The standard view is that other primates hold onto their pregnancies for longer and give birth to babies that are more developmentally advanced.

But, says Dunsworth, it is simply not true.

"We have bigger babies and longer pregnancies than you would expect," she says.

Women give birth to babies with larger brains than we would expect

In an absolute sense human pregnancies are long. They typically last 38-40 weeks, whereas a chimpanzee pregnancy is 32 weeks long, and gorillas and orang-utans give birth after about 37 weeks.

As Dunsworth and her colleagues explained in a 2012 paper, this remains true even if we adjust the pregnancy durations to take into account differences in body mass. Human pregnancies last 37 days longer than they should do for an ape our size.

The same thing applies for brain size. Women give birth to babies with larger brains than we would expect of a primate with the average woman's body mass. This means that a key prediction of Washburn's obstetric dilemma is incorrect.

There are other problems with Washburn's idea too.

A central assumption of the obstetric dilemma is that the size and shape of the human pelvis &ndash and the female pelvis in particular &ndash is highly constrained by our habit of walking upright on two legs. After all, if evolution could have "solved" the problem of human childbirth by simply making women's hips a little wider and the birth canal a little larger, it surely would have done so by now.

The birth canal is extraordinarily variable in size and shape

In 2015, Anna Warrener at Harvard University in Cambridge, Massachusetts, and her colleagues questioned this assumption.

The researchers collected metabolic data from male and female volunteers who were walking and running in the lab. Volunteers with wider hips were no more inefficient at walking and running than their narrow-hipped peers. From purely energetic considerations, at least, there does not seem to be anything stopping humans evolving wider hips that would make childbirth easier.

"The basic premise of the obstetric dilemma &ndash that having a small or narrow pelvis is best for biomechanical efficiency &ndash is likely not correct," says Helen Kurki of the University of Victoria in British Columbia, Canada.

Kurki was not involved with Warrener's study, but her own research has identified yet more problems for the traditional obstetric dilemma hypothesis.

If the female pelvis really is tightly governed by two opposing forces &ndash the need to be narrow for walking and the need to be wide for giving birth &ndash the shape of the birth canal should vary little between women. It should be "stabilised" by natural selection.

Pregnant women sometimes joke that their developing foetus feels like an energy-sapping parasite

But after analysing hundreds of human skeletons, Kurki reported in 2015 that the birth canal is extraordinarily variable in size and shape. It varies even more than the size and shape of human arms, a trait that is known to vary between individuals.

"I think my findings do support shifting attitudes to the obstetric dilemma," says Kurki.

Washburn's tidy narrative does not seem quite as satisfying as it once did. There has to be something else going on.

Dunsworth thinks she has identified one important missing piece in the puzzle: energy.

"We max out toward the end of pregnancy," says Dunsworth, herself a mother. "Those last weeks and months of pregnancy are tiring. They are pushing right against the possible sustainable metabolic rates in humans. It has to end at some point."

Evolution could, in principle, make the pelvis larger &ndash but it has not had to

Pregnant women sometimes joke that their developing foetus feels like an energy-sapping parasite. In a sense it really is, and its energy demands grow with every passing day.

In particular, human brains have an almost insatiable appetite for energy. Growing a second, tiny brain inside the womb can push a pregnant woman close to the edge, metabolically speaking.

Dunsworth calls this idea the energetics of gestation and growth (EGG) hypothesis. It suggests the timing of childbirth is governed by the difficulties of continuing to nourish a developing foetus beyond 39 weeks &ndash not by the difficulties of squeezing the baby out through the birth canal.

Dunsworth thinks people obsess too much about the tight fit between a baby's head and its mother's birth canal. It might seem too much of a coincidence that the two are so closely size-matched, but she says the pelvis has simply evolved to be the size it needs to be. Evolution could, in principle, make the pelvis larger &ndash but it has not had to.

For most of human evolution, childbirth might have been quite a lot easier

By and large, Kurki shares this view. "The obstetric canal is big enough, the majority of the time, for the foetus to pass through," she says.

This is true. But even so, take another look at the maternal mortality figures: 830 deaths every day. Even among women who do not lose their lives during childbirth, some studies say the process leads to life-changing but non-lethal injuries in as many as 40% of cases. The price women pay for childbirth seems extraordinarily high.

Wells agrees. "It's impossible to imagine the problem has been this bad over the long term."

Perhaps it has not. In 2012, Wells and his colleagues took a look at the prehistory of childbirth, and came to a surprising conclusion. For most of human evolution, childbirth might have been quite a lot easier.

The prehistory of childbirth is a difficult subject to study. The hominin pelvis is rarely preserved in the fossil record, and newborn skulls are even thinner on the ground. But from the meagre evidence available it seems that some earlier species of human, including Homo erectus and even some Neanderthals, had a relatively easy time of it when it came to giving birth.

A shift to farming may have led to developmental changes that made childbirth far more difficult

In fact, Wells and his colleagues suspect childbirth might even have been a relatively minor problem in our species &ndash at least to begin with. There are very few newborn baby skeletons among the human remains from early hunter-gatherer groups, which might hint that death rates among newborns were relatively low.

If there was a rise in newborn death rates at the dawn of farming, there were almost certainly several factors involved.

For instance, early farmers began living in relatively dense settlements, so transmissible disease probably became a far greater problem. Newborns are often particularly vulnerable when an infection is going around a community.

But Wells and his colleagues suspect a shift to farming also led to developmental changes that made childbirth far more difficult. A rise in infant mortality at the dawn of farming might be due in part to a raised risk of death during childbirth.

Human childbirth suddenly became more difficult about 10,000 years ago

There is one striking feature archaeologists have noticed when comparing the skeletons of early farmers with their hunter-gatherer ancestors. The farmers were noticeably shorter in stature, probably because their carbohydrate-rich diet was not particularly nutritious compared to the protein-rich hunter-gatherer diet.

This is a telling observation for those who study childbirth, says Wells, because there is evidence of a link between a woman's height and the size and shape of her pelvis. In general, the shorter a woman, the narrower her hips. In other words, the shift to farming almost certainly made childbirth a little bit more challenging.

On top of that, the carbohydrate-rich diets that became more common with farming can cause a developing foetus to grow larger and fatter. That makes the baby harder to deliver.

Combine these two factors and human childbirth &ndash which might have been relatively easy for millions of years &ndash suddenly became more difficult about 10,000 years ago.

Something rather like this "farming revolution effect" replays whenever human diets become poorly nutritious &ndash particularly if those diets also contain a lot of carbohydrates and sugars, which encourage foetal growth.

"We can make a simple prediction that the nutritional status of mothers should be associated with a local prevalence of maternal mortality and difficulties with giving birth," says Wells. The statistics clearly follow such a pattern, suggesting that improving nutrition might be a fairly easy way to reduce maternal mortality.

Pregnant women have adapted to nourish their foetus for as long as they can

Both Dunsworth and Kurki think that Wells has identified something significant in his work &ndash something that perhaps would only be evident to a researcher with the right background in nutrition and development.

"I'm so lucky that Jonathan is describing these complex issues from his perspective of human health," says Dunsworth. "At the same time I'm approaching the problem from my perspective of human evolution."

So we now have a new explanation for the difficulties of human childbirth. Pregnant women have adapted to nourish their foetus for as long as they can before it grows too large to feed internally. The female pelvis has adapted to be just the right size to allow this maximally-nourished foetus to travel through safely. And dietary changes in the last few thousand years have upset this fine balance, making childbirth risky &ndash particularly for mothers who have a poor diet.

However, Dunsworth says that is probably not the end of the story.

Washburn's ideas made good intuitive sense for decades, until Dunsworth, Wells, Kurki and others began to pick them apart. "What if the EGG perspective is too good to be true?" asks Dunsworth. "We have to keep searching and keep collecting evidence."

This is exactly what other researchers are doing.

For instance, in 2015 Barbara Fischer of the Konrad Lorenz Institute for Evolution and Cognition Research in Klosterneuburg, Austria and Philipp Mitteroecker of the University of Vienna, Austria took another look at the female pelvis.

A woman's pelvis takes on a shape more conducive to childbirth in her late teens &ndash when she reaches peak fertility

It seemed to them that Dunsworth's EGG hypothesis &ndash compelling though it is &ndash could actually be seen as complementary to Washburn's ideas, rather than disproving them entirely. Dunsworth agrees: she thinks many factors are involved in the evolution of modern childbirth.

Fischer and Mitteroecker investigated whether there is any correlation between female head size and pelvis size. Head size is heritable, at least to some extent, so women would benefit during childbirth if those with larger heads also naturally had a wider pelvis.

The researchers' analysis of 99 skeletons suggested such a link does indeed exist. They concluded that a woman's head size and her pelvic dimensions must somehow be linked at the genetic level.

"This does not mean that the [problem of childbirth] has been resolved," says Fischer. But the problem would be even worse if there was no link between head size and pelvis width.

And there is another complication: women's bodies change as they get older.

A May 2016 study led by Marcia Ponce de León and Christoph Zollikofer at the University of Zurich, Switzerland examined pelvic data from 275 people &ndash male and female &ndash of all ages. The researchers concluded that the pelvis changes dimensions during the course of a woman's lifetime.

Many babies are now born by Caesarean section

Their data suggested that a woman's pelvis takes on a shape more conducive to childbirth in her late teens &ndash when she reaches peak fertility. It then stays that way until around her 40th birthday, when it then gradually changes shape to become less suitable for childbirth, ready for the menopause.

The scientists suggest these changes make childbirth a little easier than it otherwise would be. They call this idea the "developmental obstetric dilemma" (DOD).

"The DOD hypothesis provides a developmental explanation for the variation in pelvic obstetric dimensions," says Ponce de León.

If all these evolutionary pressures are acting on childbirth, is the process still changing and evolving even now?

In December 2016, Fischer and Mitteroecker made headlines with a theoretical paper that addressed this question.

Earlier studies had suggested that larger babies have a better chance of survival and that size at birth is at least somewhat heritable. Together, these factors might lead the average human foetus to push up against the size limit imposed by the female pelvis, even though it can be fatal to push too far.

We all either did or didn't arrive in the world through a pelvis

But many babies are now born by Caesarean section, an operation in which the baby is taken out of the mother's abdomen without ever entering the birth canal. Fischer and Mitteroecker suggested that, in societies where C-sections have become more common, foetuses can now grow "too large" and still have a reasonable chance of survival.

In theory, as a consequence the number of women giving birth to babies that are too big to fit through their pelvis might have risen by 10 or 20% in just a few decades, at least in some parts of the world. Or, to put it in cruder terms, people in these societies might be evolving to have larger babies.

For now this is only an idea and there is no hard evidence that it is really happening. But it is an intriguing thought.

"We all either did or didn't arrive in the world through a pelvis," says Wells. "If we did, that pelvis mattered. And if we didn't, that in itself is interesting."

Ever since live birth evolved, babies have been constrained to some degree by the size of the birth canal. But maybe, for some babies at least, that is no longer true.

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A randomized controlled clinical trial of interventions to promote prenatal screening for GBS was conducted. The participant service was a major private health insurance company managed by a medical cooperative in Porto Alegre, South Brazil [16]. All obstetricians (n = 241) who had provided outpatient prenatal care and assisted in at least one delivery (vaginal or cesarean section) covered by this health insurance in the 3 months before the study (April to June, 2008) were invited to take part. The same doctors were involved in prenatal care. The participant obstetricians were allocated randomly into three groups: direct mail (DM, n = 76), AD (n = 76) and control (C, n = 89). A list of random numbers generated by the Statistical Package for the Social Sciences (SPSS Inc., Chicago, IL, USA) was used to allocate the obstetricians.

The DM intervention comprised printed guidelines on antenatal GBS screening sent by post to the obstetrician’s private office in July, 2008. The AD intervention included these guidelines and a 30-minute face-to-face education-oriented interview on antenatal GBS screening based on the national guidelines for antenatal care [2]. This was conducted by a trained physician and took place in the private offices of the participating obstetricians, in July and August, 2008. No intervention was provided to the C group.

The electronic database of the participating organization was used to gather the following information about the obstetricians and their performance of antenatal care and deliveries both 3 months pre-intervention (April to June, 2008) and 3 months post-intervention: obstetrician age, gender, year of graduation in medicine, number of years of antenatal clinical practice in the medical cooperative, number of births assisted, and the frequency of GBS screening requested.

Multivariable Poisson regression analysis was used to investigate the effect of the intervention on the proportion of pregnant women tested for GBS, controlling for potential confounding factors (physician age and sex, time since graduation in medicine and number of years of antenatal clinical practice in the medical cooperative). A P value of 0.05 or less was considered statistically significant.

The study was approved by the Ethics Committee of Federal University of Rio Grande do Sul, protocol number 2007792.

How Did Humans Figure Out That Sex Makes Babies?

Photo by Janek Skarzynski/AFP/Getty Images.

When the Explainer asked you to vote on a favorite unanswered question of 2012, the majority opted for a rather lascivious query regarding why rich ladies sunbathe topless, and the Explainer has duly delivered your pound of flesh. But in perusing the runners-up, another question so intrigued the Explainer that he could not resist answering it as well: When and how did humankind figure out that sex is what causes babies? It’s not exactly the most obvious correlation: Sex doesn’t always lead to babies, and there’s a long lead time between the act and the consequences—weeks before there are even symptoms, usually. So roughly where do we think we were as a species when it clicked?

Basically, since the beginning. While anthropologists and evolutionary biologists can’t be precise, all available evidence suggests that humans have understood that there is some relationship between copulation and childbirth since Homo sapiens first exhibited greater cognitive development, sometime between the emergence of our species 200,000 years ago and the elaboration of human culture probably about 50,000 years ago. Material evidence for this knowledge is thin, but one plaque from the Çatalhöyük archaeological site seems to demonstrate a Neolithic understanding, with two figures embracing on one side and a mother and child depicted on the other. A firmer conclusion can be drawn from the fact that, though explanations for conception vary wildly across contemporary cultural groups, everyone acknowledges at least a partial link between sex and babies.

As for how humans attained what biological anthropologist Holly Dunsworth calls “reproductive consciousness,” that part is murkier. Most likely, we got the gist from observing animal reproduction cycles and generally noting that women who do not sleep with men do not get pregnant. But that doesn’t mean that early peoples—or for that matter, modern people—thought or think of the process in the utilitarian, sperm-meets-egg way that the scientifically literate do now.

Around the turn of the 20 th century, anthropologists working in places such as Australia and New Guinea reported that their subjects did not recognize a connection between sex and children. However, subsequent research has shown these biased reports to be only half-true at best. For example, Bronislaw Malinowski claimed in 1927 that, for Trobriand Islanders, the father played no role in producing a child. But later anthropologists studying the same group learned that semen was believed to be necessary for the “coagulation” of menstrual blood, the stoppage of which was thought to eventually form the fetus.

Even though the Trobriand Islanders’ traditional explanations of conception seem quaint or strange, they do on some level recognize the tie between sex and childbirth. And of course, before we Westerners get to feeling all superior, it must be said that our notions of conception are not wholly consistent or rational either. (The number of unplanned pregnancies in the United States reveals as much.) As women’s studies scholar Cynthia Eller points out, while “other events may also be necessary—such as the entrance of a spirit child through the top of the head (in the case of the Triobriand Islanders), or the entrance of a soul into a fertilized egg (in the case of Roman Catholics) … it is simply not believed that women bear children without any male participation whatsoever.”

If we humans have essentially always kind of understood that the deed leads to the delivery room, did that knowledge have any consequences on our evolution as a society? Holly Dunsworth argues that, of the entire animal world, “reproductive consciousness” is unique to humans. That special knowledge may help explain both the evolution of our taboos around sex and our ability to bend nature’s procreative capacities to our favor in everything from dog-breeding to family planning.

Explainer thanks Holly Dunsworth of the University of Rhode Island, Cynthia Eller of Montclair State University, Helen Fisher of Rutgers University, and Wenda Trevathan of New Mexico State University.

Development of the baby

A new human life is started (conceived) in the zygote at the moment of fertilisation, but in the resulting ball of cells there is practically no difference between the cells.
As it grows into an embryo - the cells become specialised for various functions ( differentiation ) as different body structures become distinct.
From about 8 weeks onwards, it is technically called a foetus. More and more features of the human body become noticeable, even though the foetus itself is small. As the foetus grows, the mother's uterus expands. Usually, the foetus eventually ends up in a head downwards position, and this needs to be checked.
At ante-natal clinics, other checks are carried out in order to monitor the progress of the pregnancy.
These usually include:
- externally checking the growth of the developing foetus by measuring the size of the mother's abdomen
- using a stethoscope to listen to the baby's heartbeat
- monitoring of mother's blood pressure and blood haemoglobin
- possibly more advanced techniques such as ultrasound scanning, which produces a "picture" of the baby in the uterus.

If required, cells may be removed from the liquid surrounding the embryo (amniocentesis) or from the placenta (chorionic villi sampling-CVS), and these may be used in screening for certain genetic diseases. These are fairly simple operations, but not without risks to the developing foetus.

It is also worth noting that these services are only available in the developed countries.
Elsewhere, childbirth remains more problematic.

The development of the baby

Disease organism or chemical
substance crossing placenta
Possible effect on baby
german measles (Rubella) nervous system problems -
smaller birth weight
CO/ nicotine from
smaller birth weight
birth defects - deformed/reduced


Flexible sacrum birthing position has effect on reduction in duration of the second stage of labor with a considerable variation was reported. This reduction in duration of second stage of labor should be discussed among health care providers who care for women during labor and childbirth.


Laboring women should be encouraged to choose a birth positions that she finds comfortable. Researchers who aim to compare different birth positions should consider study designs which enables women to choose birthing position.

Prenatal Care

During pregnancy, prenatal examinations guide doctors and parturients about the baby’s development.

Ultrasounds are performed in each trimester of pregnancy to find out the weight and size of the fetus and identify malformations in addition, blood tests and other specific tests are performed for pregnant women.

Ultrasound of a fetus around the 4th month of pregnancy.

The medical team must guide and clarify the doubts of the pregnant woman and her partner, who must decide the best way for the birth of their baby.

WHO recommendations

According to the World Health Report of WHO (World Health Organization) released in 2005, prenatal consultations are essential to plan delivery and prepare the mother for motherhood.

In addition, this can be an important time to start family planning , advising on the choice of having more children and the right time to do so, contraceptive methods, and also on sexually transmitted disease (STD) control programs and on child malnutrition.

Fear of Childbirth

Childbirth is a very important moment in anyone’s life, the birth of a new being marks the beginning of many responsibilities for parents and a lot of happiness for the whole family.

Despite being a natural phenomenon, childbirth is surrounded by taboos and myths that are passed on from generation to generation and stimulated in the media.

This generates many doubts and fears in women: fear of pain, fear of the baby dying, fear of not being able to. Every woman should know her own body and receive support (from the medical team, partner, family, etc.) to choose the best way to give birth to her baby .

There are several types of delivery , the main ones being: normal, squatting, in water, cesarean section, induced, using forceps, among others.

Normal birth

Stages of normal delivery

Normal delivery, as its name implies, happens naturally respecting the physiological process.

There is no need for medication, but many women receive anesthesia to control pain, relax and dilate more quickly.

The labor contractions and starts with the neck of the uterus expands until it allows the passage of the fetus through the vaginal canal after the placenta is expelled.

Cesarean section

Cesarean or cesarean delivery is a surgical procedure in which the fetus is removed by an abdominal cut.

It is indicated for situations where there is a risk of life for the mother or baby.

This applies in serious situations such as: eclampsia that causes seizures in the mother, placenta previa that prevents the baby from passing through or when the baby shows signs of fetal distress.

Doctor removing a baby during a caesarean section.

Elective cesareans, that is, performed at the option of the parturient and not in situations of risk, can have complications such as hemorrhages and infections.

They are often performed before labor begins, based on the expected date of birth, so that in some cases they are premature delivery.

Induced Birth

Childbirth can be induced through the administration of substances, with synthetic oxytocin being used, similar to the hormone naturally produced by the maternal body during childbirth.

It is usually performed when labor does not progress and the woman has no dilation, for example, in cases of pregnancies exceeding 40 weeks, and specific conditions.

It is used as an attempt to perform a normal delivery and to avoid having a cesarean section, and the excessive use of oxytocin and the delay in carrying out delivery can cause problems in the uterus and fetal distress.

Forceps Delivery

Delivery can be performed using specific instruments such as forceps.

It is introduced into the vagina and positioned on the sides of the fetus’ head in order to pull it out and facilitate its exit.

There are several reports of injuries to the mother and baby caused by the use of forceps, however, doctors guarantee that it is a safe way.

Humanized birth

In humanized delivery, the health professionals involved respect the moment the baby is born and avoid unnecessary interventions, such as cutting the perineum called an episiotomy, doing intestinal washes, using synthetic oxytocin to accelerate delivery, among others.

It is a process that involves different types of childbirth, and can be performed at the hospital, in delivery houses or at the parturient’s home (home birth).

Born This Way?

Illustration by Charlie Powell

“Baby, you were born this way.” As soon as Lady Gaga sang these words on her smash hit “Born This Way,” they became a rallying cry for gay people around the world, an anthem for sexual minorities facing discrimination. The shiny, catchy song carries an empowering (if simple) message: Don’t be ashamed about being gay, or bi, or trans, or anything—that’s just how you were born. Gaga later named her anti-bullying charity after the same truism, and two filmmakers borrowed it for their documentary exposing homophobia in Africa. A popular “Born This Way” blog encourages users to submit reflections on “their innate LGBTQ selves.” Need a quick, pithy riposte against anti-gay bigotry? Baby, we were born this way.

But were we? That’s the foundational question behind the gay rights movement—and its opponents. If gay people were truly born that way, the old canard of homosexuality as a “lifestyle choice” (or “sexual preference”) is immediately disproven. But if gay people weren’t born that way, if scientists were unable to find any biological basis for sexual orientation, then the Family Research Council crowd could claim vindication in its fight to label homosexuality unnatural, harmful, and against nature.

In recent years, scientists have proposed various speculative biological bases for homosexuality but never settled on an answer. As researchers draw closer to uncovering an explanation, however, a new question has arisen: What if in some cases sexuality is caused by an identifiable chemical process in the womb? What if, in other words, homosexuality can potentially be prevented? That is one implication of one of the most widely accepted hypotheses thus far proposed. And if it’s true, it could turn out to be a blow for the gay rights movement.

Some of the strongest current evidence that some people are born gay is based on a phenomenon called the fraternal birth order effect. Several peer-reviewed studies have shown that men with older biological brothers are likelier to be gay than men with older sisters or no older siblings. The likelihood of being gay increases by about 33 percent with each additional older brother. From these statistics, researchers calculate that about 15 to 30 percent of gay men have the fraternal birth order effect to thank for their homosexuality.

The fraternal birth order effect is a little perverse. It means that a disproportionate number of gay men are born into disproportionately homophobic households. Couples with large numbers of children tend to be religious and belong to denominations that are conservative and more homophobic. Consider the numbers: 1 percent of Unitarians have four or more children, while 3 percent of evangelical Protestants, 4 percent of Catholics, 6 percent of Muslims, and 9 percent of Mormons have families that large. At the same time, 64 percent of Evangelicals, 30 percent of Catholics, 61 percent of Muslims, and 68 percent of Mormons believe homosexuality should be “discouraged by society.” (Compare that with 15 percent of Jews.) Big families that disapprove of gay people are likely to have gay people in their own clan.

Perhaps these families would be more accepting if the specific biological basis for the birth order effect were elucidated. We know the effect is biological rather than social—it’s entirely absent in men whose older brothers were adopted—but scientists haven’t been able to prove much else. One of the leading explanations is called the maternal immunization hypothesis. According to Ray Blanchard of the University of Toronto, when a woman is pregnant with a male fetus, her body is exposed to a male-specific antigen, some molecule that normally turns the fetus heterosexual. The woman’s immune system produces antibodies to fight this foreign antigen. With enough antibodies, the antigen will be neutralized and no longer capable of making the fetus straight. These antibodies linger in the mother’s body long after pregnancy, and so when a woman has a second son, or a third or fourth, an army of antibodies is lying in wait to zap the chemicals that would normally make him heterosexual.

Or so Blanchard speculates. Although the hypothesis sounds reasonable enough, it’s premised on a number of assumptions that haven’t been proven. For instance, no one has shown that there is a particular antigen that controls sexual orientation, let alone one designed to make men straight. And if that antigen does exist, does it control orientation only? Blanchard refers to its antibody attackers as “anti-male,” implying that the antigen controls for various aspects of masculinity. But when I asked him about this, he was noncommittal. Moreover, the hypothesis proposes a loose, two-way flow of antigens and antibodies between the fetus (whose antigens spread to the mother) and the mother (whose antibodies spread to the fetus). But this exchange has never been observed—and the antibodies and antigens in question are hypothetical, anyway. If they do exist, there’s no assurance that they perform this placental pirouette.

There’s a problem with this explanation. Even though the gay rights movement theoretically wants proof that homosexuality is inborn, this particular hypothesis is, unintentionally, a little insulting. “The scientists behind the [maternal immunization] hypothesis talk about it as if they’re not making judgments, but there are implicit judgments,” says Jack Drescher, former chair of the American Psychiatric Association’s Committee on Gay, Lesbian, and Bisexual Issues. Drescher points out, correctly, that the hypothesis is fundamentally one of pathology. If Blanchard is right, then (at least some) gay people are indeed born gay, but there’s still something wrong with them. The hypothesis turns homosexuality into a birth defect, an aberration: Gay people are deviants from the normative mode of heterosexuality. We may have been born this way, the hypothesis implies, but that’s not how it was supposed to happen.

Drescher is skeptical that scientists will ever uncover a single biological basis for homosexuality—he suspects the root causes are more varied and complex—and suggests that it’s the wrong question to ask in the first place. But the hunt will go on. The gay rights movement, like the black civil rights movement before it, begins with the proposition that we should not discriminate against people because of who they are or how they were born. That’s a belief most Americans share, and it explains the success of the “born this way” anthem. If homosexuality is truly biological, discrimination against gay people is bigotry, plain and simple. But if it’s a birth defect, as Blanchard’s work tacitly suggests, then being gay is something that can—and presumably should—be fixed.

That’s a toxic view, and one that must be abandoned. We might not yet understand the exact biological mechanisms underlying sexual orientation, but we will one day soon. And if, at that point, homosexuality is seen as a disorder, the next step will be a search for a cure. That would be a tragedy—for society and for science. There’s nothing wrong with being gay: You know it I know it the Supreme Court knows it. But so long as large swaths of the country believe otherwise—places where homophobic families still ostracize their gay sons and brothers—any research into its biological origins is fraught with peril for the cause of gay rights.


Pregnancy causes physiologic changes in all maternal organ systems most return to normal after delivery. In general, the changes are more dramatic in multifetal than in single pregnancies.


Cardiac output (CO) increases 30 to 50%, beginning by 6 weeks gestation and peaking between 16 and 28 weeks (usually at about 24 weeks). It remains near peak levels until after 30 weeks. Then, CO becomes sensitive to body position. Positions that cause the enlarging uterus to obstruct the vena cava the most (eg, the recumbent position) cause CO to decrease the most. On average, CO usually decreases slightly from 30 weeks until labor begins. During labor, CO increases another 30%. After delivery, the uterus contracts, and CO drops rapidly to about 15 to 25% above normal, then gradually decreases (mostly over the next 3 to 4 weeks) until it reaches the prepregnancy level at about 6 weeks postpartum.

The increase in CO during pregnancy is due mainly to demands of the uteroplacental circulation volume of the uteroplacental circulation increases markedly, and circulation within the intervillous space acts partly as an arteriovenous shunt. As the placenta and fetus develop, blood flow to the uterus must increase to about 1 L/min (20% of normal CO) at term. Increased needs of the skin (to regulate temperature) and kidneys (to excrete fetal wastes) account for some of the increased CO.

To increase CO, heart rate increases from the normal 70 to as high as 90 beats/min, and stroke volume increases. During the 2nd trimester, blood pressure (BP) usually drops (and pulse pressure widens), even though CO and renin and angiotensin levels increase, because uteroplacental circulation expands (the placental intervillous space develops) and systemic vascular resistance decreases. Resistance decreases because blood viscosity and sensitivity to angiotensin decrease. During the 3rd trimester, BP may return to normal. With twins, CO increases more and diastolic BP is lower at 20 weeks than with a single fetus.

Exercise increases CO, heart rate, oxygen consumption, and respiratory volume/min more during pregnancy than at other times.

The hyperdynamic circulation of pregnancy increases frequency of functional murmurs and accentuates heart sounds. X-ray or ECG may show the heart displaced into a horizontal position, rotating to the left, with increased transverse diameter. Premature atrial and ventricular beats are common during pregnancy. All these changes are normal and should not be erroneously diagnosed as a heart disorder they can usually be managed with reassurance alone. However, paroxysms of atrial tachycardia occur more frequently in pregnant women and may require prophylactic digitalization or other antiarrhythmic drugs. Pregnancy does not affect the indications for or safety of cardioversion.


Total blood volume increases proportionally with cardiac output, but the increase in plasma volume is greater (close to 50%, usually by about 1600 mL for a total of 5200 mL) than that in red blood cell (RBC) mass (about 25%) thus, hemoglobin (Hb) is lowered by dilution, from about 13.3 to 12.1 g/dL. This dilutional anemia decreases blood viscosity. With twins, total maternal blood volume increases more (closer to 60%).

White blood cell count (WBC) count increases slightly to 9,000 to 12,000/mcL. Marked leukocytosis ( ≥ 20,000/mcL) occurs during labor and the first few days postpartum.

Iron requirements increase by a total of about 1 g during the entire pregnancy and are higher during the 2nd half of pregnancy—6 to 7 mg/day. The fetus and placenta use about 300 mg of iron, and the increased maternal RBC mass requires an additional 500 mg. Excretion accounts for 200 mg. Iron supplements are needed to prevent a further decrease in Hb levels because the amount absorbed from the diet and recruited from iron stores (average total of 300 to 500 mg) is usually insufficient to meet the demands of pregnancy.


Changes in renal function roughly parallel those in cardiac function. Glomerular filtration rate (GFR) increases 30 to 50%, peaks between 16 and 24 weeks gestation, and remains at that level until nearly term, when it may decrease slightly because uterine pressure on the vena cava often causes venous stasis in the lower extremities. Renal plasma flow increases in proportion to GFR. As a result, blood urea nitrogen (BUN) decreases, usually to < 10 mg/dL ( < 3.6 mmol urea/L), and creatinine levels decrease proportionally to 0.5 to 0.7 mg/dL (44 to 62 micromole/L). Marked dilation of the ureters (hydroureter) is caused by hormonal influences (predominantly progesterone ) and by backup due to pressure from the enlarged uterus on the ureters, which can also cause hydronephrosis. Postpartum, the urinary collecting system may take as long as 12 weeks to return to normal.

Postural changes affect renal function more during pregnancy than at other times ie, the supine position increases renal function more, and upright positions decrease renal function more. Renal function also markedly increases in the lateral position, particularly when lying on the left side this position relieves the pressure that the enlarged uterus puts on the great vessels when pregnant women are supine. This positional increase in renal function is one reason pregnant women need to urinate frequently when trying to sleep.


Lung function changes partly because progesterone increases and partly because the enlarging uterus interferes with lung expansion. Progesterone signals the brain to lower carbon dioxide (CO2) levels. To lower CO2 levels, tidal and minute volume and respiratory rate increase, thus increasing plasma pH. Oxygen consumption increases by about 20% to meet the increased metabolic needs of the fetus, placenta, and several maternal organs. Inspiratory and expiratory reserve, residual volume and capacity, and plasma PCO2 decrease. Vital capacity and plasma PCO2 do not change. Thoracic circumference increases by about 10 cm.

Considerable hyperemia and edema of the respiratory tract occur. Occasionally, symptomatic nasopharyngeal obstruction and nasal stuffiness occur, eustachian tubes are transiently blocked, and tone and quality of voice change.

Mild dyspnea during exertion is common, and deep respirations are more frequent.

Gastrointestinal (GI) and hepatobiliary

As pregnancy progresses, pressure from the enlarging uterus on the rectum and lower portion of the colon may cause constipation. GI motility decreases because elevated progesterone levels relax smooth muscle. Heartburn and belching are common, possibly resulting from delayed gastric emptying and gastroesophageal reflux due to relaxation of the lower esophageal sphincter and diaphragmatic hiatus. Hydrochloric acid production decreases thus, peptic ulcer disease is uncommon during pregnancy, and preexisting ulcers often become less severe.

Incidence of gallbladder disorders increases somewhat. Pregnancy subtly affects hepatic function, especially bile transport. Routine liver function test values are normal, except for alkaline phosphatase levels, which increase progressively during the 3rd trimester and may be 2 to 3 times normal at term the increase is due to placental production of this enzyme rather than hepatic dysfunction.


Pregnancy alters the function of most endocrine glands, partly because the placenta produces hormones and partly because most hormones circulate in protein-bound forms and protein binding increases during pregnancy.

The placenta produces the beta subunit of human chorionic gonadotropin (beta-hCG), a trophic hormone that, like follicle-stimulating and luteinizing hormones, maintains the corpus luteum and thereby prevents ovulation. Levels of estrogen and progesterone increase early during pregnancy because beta-hCG stimulates the ovaries to continuously produce them. After 9 to 10 weeks of pregnancy, the placenta itself produces large amounts of estrogen and progesterone to help maintain the pregnancy.

The placenta produces a hormone (similar to thyroid-stimulating hormone) that stimulates the thyroid, causing hyperplasia, increased vascularity, and moderate enlargement. Estrogen stimulates hepatocytes, causing increased thyroid-binding globulin levels thus, although total thyroxine levels may increase, levels of free thyroid hormones remain normal. Effects of thyroid hormone tend to increase and may resemble hyperthyroidism, with tachycardia, palpitations, excessive perspiration, and emotional instability. However, true hyperthyroidism occurs in only 0.08% of pregnancies.

The placenta produces corticotropin -releasing hormone (CRH), which stimulates maternal adrenocorticotropic hormone (ACTH) production. Increased ACTH levels increase levels of adrenal hormones, especially aldosterone and cortisol, and thus contribute to edema.

Increased production of corticosteroids and increased placental production of progesterone lead to insulin resistance and an increased need for insulin , as does the stress of pregnancy and possibly the increased level of human placental lactogen. Insulinase, produced by the placenta, may also increase insulin requirements, so that many women with gestational diabetes develop more overt forms of diabetes.

The placenta produces melanocyte-stimulating hormone (MSH), which increases skin pigmentation late in pregnancy.

The pituitary gland enlarges by about 135% during pregnancy. The maternal plasma prolactin level increases by 10-fold. Increased prolactin is related to an increase in thyrotropin -releasing hormone production, stimulated by estrogen . The primary function of increased prolactin is to ensure lactation. The level returns to normal postpartum, even in women who breastfeed.


Increased levels of estrogens , progesterone , and MSH contribute to pigmentary changes, although exact pathogenesis is unknown. These changes include

Melasma (mask of pregnancy), which is a blotchy, brownish pigment over the forehead and malar eminences

Darkening of the mammary areolae, axilla, and genitals

Linea nigra, a dark line that appears down the midabdomen

Melasma due to pregnancy usually regresses within a year.

Incidence of spider angiomas, usually only above the waist, and of thin-walled, dilated capillaries, especially in the lower legs, increases during pregnancy.


This photo shows brown patches on the cheeks of a patient with melasma.


© Springer Science+Business Media

A linea nigra is a dark line that appears down the midabdomen during pregnancy.

© Springer Science+Business Media

Image provided by Thomas Habif, MD.

Spider angiomas (nevus araneus) are small, bright red spots that are surrounded by tiny blood vessels (capillaries), which resemble spider legs. After releasing pressure sufficient to blanch them, they refill from the central area. They are normal in many healthy people. They commonly develop in women who are pregnant or use oral contraceptives and in people who have cirrhosis of the liver.

Watch the video: The Birth: Labor, Delivery, u0026 Early Postpartum PaO - Childbirth Series (August 2022).