Dernière version du 27 février 2009 à 08:32

What is pregnancy?

For human beings, pregnancy occurs amongst the female, taking place precisely in the uterus. It is the state of carrying one or more embryos that will eventually develop into a foetus, during a period of nine months. This period starts at conception and ends at the point of delivery.

How does pregnancy occur?

Pregnancy takes place after fertilization, which usually occurs in the the fallopian tube, near the uterus. The sperm cells travel up the cervix and into the uterus in search of the egg. Once in the uterus, the uterus contracts and helps the sperm enter into the fallopian tubes, which are situated above. Conception takes place when the egg and a sperm cell come into contact to form a zygote. Pregnancy occurs by the implantation of the embryo (which is at this stage a ball of rapidly multiplying cells called the blastocyst) into the uterus about three or four days after fertilization.The embryo attaches itself to the uterine wall ( which is also called the uterine lining) and will then develop and grow inside the uterus for a period of nine months (about 266 days) and during this time, various changes occur in the mother's body in order to accomodate the growing fetus.
Pregnancy is divided into three trimesters, each of which lasting about three months each. These trimesters help us to monitor not only the growth of the baby and the mother but also the changes occuring inside the mother's body. Although complications such as miscarriages can occur, the foetus usually grows healthily during pregnancy, recieving its nutrients from it's mother and growing in a safe and comfortable environnement which is the uterus.

What are the different stages of pregnancy?

First trimester

The first trimester includes fertilization and implantation. During the very first weeks of this period the embryo's nutrients are supplied by the endometrium ( whose role is to be the uterus's lining). The placenta later develops, containing embryonic and maternal blood vessels. The combination of these two becomes the new supplier of nutrients and also the provider of the immune protection. The placenta also exchanges respiratory gases and gets rid of the wastes that are produced by the embryo. During the process of splitting which usually occurs in the first month of pregnancy, the embryo can divide itself into identical (or monozygotic) twins. This first trimester is the time when the fetus's body organs develop, this is called organogenesis. The fetus is usually very fragile during organogenesis, which is why the mother is advised not to take drugs and to stay away from radiation in order to avoid birth defects.

During this period, the most important changes also concerning the mother occur. The mother may experience problems such as excessive vomiting, weight gain, heartburn, dizziness and tiredness due to these changes. Nausea and vomiting are usually very common and are probably the first symptoms of pregnancy the mother will experience.
These changes experienced by the mother are due to the growth of the embryo, which by about the eighth week of pregnancy, would have a developing brain, tiny arms and legs and even a heartbeat. This means that from the eighth week, an ultrasound of the embryo can be taken and the embryo can now be called a fetus.
By week twelve, almost all the fetus' limbs are developed. It is possible to find out at this stage if the fetus will be a boy or a girl because it's sexual organs would have started developing.
At the end of the trimester, which usually lasts for about thirteen weeks, the mother will stop experiencing vomiting and nausea and her energy levels will go back to normal but she will start experiencing headaches due to the greater pumping of blood by her enlarged heart.

see Annex Pregnancy_Childbirth 1
see Annex Pregnancy_Childbirth 2 & 3

Second trimester

The main changes consisting the fetus's development during the second trimester involve the fetus's change of size and the general improvement of its human features. At this stage the pregnancy becomes more obvious because of the growth of the baby. People can easily notice that the mother is pregnant.

The Annex 4 shows a fetus at 14 weeks, 2 weeks into the second trimester. The fetus is now about 6 cm long.

At week twenty, the fetus now weighs about half a kilogram, and has the developed face of an infant. Its arms, legs, fingers and toes have now lengthened. By this time, the fetus's heartbeat can be detected with a stethoscope, and the fetus is usually quite active which is why the mother may often feel her baby move. The fetus can now bend forward into the fetal position, with its head bent against its knees, because of the limited space in the uterus. By the end of the second trimester, the fetus's eyes have opened fully and it's teeth have formed.

At this stage the mother's energy will start to return but she may start to experience back pains and leg muscles cramps, but this stage isn't very uncomfortable compared to the next trimester to come.

Third trimester

The third trimester starts at week twenty eight and ends at week forty-one. It is a time of rapid growth as the fetus gains the strength it will need to survive outside the protective environment of the uterus. The fetus's activity decreases at this stage because it is in the process of fully occupying all the available space. The uterus, in turn, eventually expands as the fetus grows, so as to accommodate the fetus's bigger size.
During this time, the mother's abdominal organs compress and they are displaced causing her to urinate frequently, have digestive blockages and experience strain in her back muscles. At this stage of pregnancy, it is very important for the mother to eat regularly because of the fetus' rapid growth. Its muscles and lungs (the fetus's respiratory system will develop so that the baby can practice breathing) are under development and it's head is growing bigger to accommodate it's rapidly developing brain. It can now blink its eyes (which now have lashes), and With its eyesight developing, it may be able to see the light that penetrates the mother's womb. The fetus gains the ability to maintain its own temperature, it also loses a lot of its hair, except on its head. This trimester, the baby needs about 250 milligrams of calcium each day to strengthen its hardening bones. This is why it is very important for the mother to eat well, mainly calcium based products.

The mother also experiences, during this period, some uncomfortable symptoms. She will experience some swelling on her feet and ankles and also on her eyelids. Her uterus will expand beneath her diaphragm, the muscle just below the lungs, and this is likely to cause her to easily run out of breath. She is also likely to experience what is called the Braxton Hicks contractions. These contractions are nothing compared to the real thing. They're just warm-ups for the real thing which is why they're painless and come and go unpredictably. True labor contractions get longer, stronger and closer together. Another obvious symptom of pregnancy is the mother's weight gain. This is due to the baby's own weight but the placenta, the amniotic fluid, much larger breasts and uterus, extra fat stores, and increased blood and fluid volume also contribute to this weight gain.

Babies born prematurely-as early as 24 weeks- may survive, but they require special medical care after birth. Different techniques of childbirth will be seen later.

The fetus usually rotates so that its head points down towards the cervix. If it doesn't, the process of birth can be much more difficult. The mothers' abdominal organs may be squashed, causing frequent urination,digestive troubles,and back-aches. At birth (Annex 6) ,babies are about 50 cm in length and they weigh about 2.0-4.5 kg.

How is pregnancy monitored?

While pregnancy is a completely natural phenomenon, it however needs to be followed by health care professionals in order to discover the best possible outcome. Monitoring pregnant women is part of the prenatal care which gives the doctor a chance to monitor and check on the mother's health as well as the progress of her pregnancy and its well-being. The tests that are used to monitor pregnancy usually look for any abnormalities concerning the fetus's movement, rate of growth and heartbeat. These tests can either show an image of the fetus in it's mother's womb or they can reproduce a sound or a recording of the fetus's heartbeat. The quality of such prenatal monitoring and delivery care greatly influences a child's growth and development. In the interest of reducing levels of perinatal and maternal mortality the pregnancy has to be followed by professionals who will use different techniques, such as:

The kick count

Pregnant women do not really need professionals to perform this test. They can usually do it by themselves but what they do need is a professional's instruction on how to take the test. This test helps the doctor and the mother to keep track of the fetus's movements. It consists in keeping a kick count at the period of late pregnancy. All the mother has to do is write down the number of times the fetus moves over a certain period of time. The doctor usually explains the significance of the results to the mother. If the fetus does not move during a period of twelve hours, this could mean that there is something wrong with it. In this case, more complex tests can be taken.

An ultrasound exam This test permits the doctor to have pictures (which are called sonograms) of the fetus. These pictures which are made from sound waves help the doctor to know if the fetus is healthy. The special device needed to have an ultrasound is responsible for sending the waves to the uterus. These waves are then echoed back from the fetus and then turned into an image (which represents the fetus) on a monitor. The device needed to have an ultrasound is called a transducer. A handheld transducer can be moved about on the mother's stomach or a vaginal transducer (which is placed in the vagina) can be used instead.

Some ultrasound tests (called Doppler ultrasound tests) use sound waves that form signals of the fetus's heartbeat. These signals are represented on a graph instead of being represented in the form of pictures on a monitor. It is possible for ultrasound exams to be combined with other tests so that the professionals can learn more about the fetus's health and growth but they are also quite effective when used alone.

Ultrasound exams are not at all dangerous and they cannot harm the mother or the fetus, which is why they are used in all major hospitals and in many doctors' offices.

The nonstress test A fetus's heart is supposed to beat faster when it moves. This test measures the fetus's heart rate when it moves. To perform this test, the doctor will put a belt around the mother's abdomen and then he will attach transducers to the belt. The test usually takes between twenty to forty minutes. During this time, the fetus's heart rate is measured with a Doppler ultrasound. The mother will be asked to press a button every time she feels her baby move and the results are noted on a recording paper. This permits the experts to compare the fetus's heart rate when it moves with its heart rate when it is still.

In a case where the fetus does not move for a long period of time during the nonstress test, it does not necessary mean there is a problem because the fetus might just be asleep. In these cases, the doctor may wake the fetus up artificially or he may ask the mother to eat or drink.

This test could give false alarms. This means that it could indicate that there is a problem when there is nothing wrong. If the test indicates no change in the fetal heart rate when it moves, the doctor will probably want to take another more advanced test so as to be sure the first results ar right.

Contraction stress test

The contraction stress test is taken towards the end of pregnancy to discover if the fetus can bear with the contractions that take place during childbirth. It indicates the fetus's heart rate when the mother's uterus contracts. These contractions are not natural, they are induced while the test is being taken. This is why they are nothing like the real thing, instead they are practically painless although they cause less blood (than usual) to flow to the placenta. To provoke these contractions, a small dose of a drug called oxytocin could be injected into her veins or she could be asked to gently massage one of her nipples.

Like in the nonstress test, a Doppler ultrasound is also used in this test to measure the fetus's heart rate. This test could take between an hour and two hours. A good positive result to the contraction stress test means that the fetus is getting a good amount of oxygen.

The biophysical profile

This is a combination of an ultrasound and a nonstress test. Normally, five different points concerning the fetus are studied:

The fetus's heart rate

The fetus's breathing

The fetus's muscle tone

The fetus's body movement

The amount of amniotic fluid surrounding the fetus inside the uterus

These different points are all given a score. All the scores will be added up to make a total. This total will indicate if the fetus is in any danger and if so, special care or early delivery are likely to be the possible options.

When are advanced tests needed?

Some prenatal tests like blood tests, urine tests and blood pressure checks are routine tests. This means that every pregnant woman has to take them. But some women may be asked to take more tests so as to check the development and the health of their baby. This situation mainly depends on the stage of the pregnancy, the mother's health history and the results of the routine tests. This is because some women have a higher risk of having certain difficulties or problems due to a medical condition during pregnancy. These women need to be monitored very closely, a lot more than other women. The possible medical conditions that could cause the need for more monitoring and advanced tests are:

High blood pressure
Diabetes
Post-term pregnancy ( which is pregnancy that still continues two weeks after the due date)
Too much or too little amniotic fluid in the uterus
Kidney or heart disease
The presence of two or more fetuses in the uterus

When any of these cases occur, the health care expert is likely to perform an ultrasound exam, the nonstress test, the contraction stress test, or the biophysical profile because they all provide the useful information that is needed to determine the best treatment needed to keep both the mother and the fetus as healthy as possible.

The fetus can also be monitored during labor with similar but complex devices, most of which are placed in the mother's vagina. These devices have the same goal as the devices that are used during pregnancy. Their goal is to make sure the mother stays healthy and the develops properly.

What are the possible complications during pregnancy?

There are some possible complications that could occur to both the mother and her baby during pregnancy.

There a quite often "routines" complications. Like after 4 or 5 weeks of pregnancy, there could be some repercussions on the mother's spinal column. This is due to the gain of weight and the volume increase of the uterus. This is why pregnant women are usually advised not to stay standing for a long time and not to carry heavy things. Other small problems could occur during pregnancy like occasional and irregular contractions which are due to dehydration.

But there are some other more serious complications like the ectopic pregnancy. It is when the fertilized egg isn't implanted in the uterine wall but in another tissue. The egg can be implanted either in the Fallopian tube, or in cervix. Less frequently it can also be implanted in the ovaries or the abdomen. This abnormality is due to the enzymes produced by the fetus and which allow it to develop itself in varied types of tissues. But further, great tissue damage can be caused to an embryo implanted elsewhere than in the uterus because of the non-sufficient supply of blood. The ectopic pregnancy is very dangerous for the mother who has no choice but to abort.

Another type of complication is anemia. This happens when the mother doesn't have enough blood cells in her blood. A lot of women can go through this complication but it is a complication that doesn't usually harm the fetus.

High blood pressure or hypertension, could also be a complication. This can happen when the mother's blood pressure is very high before pregnancy. But it can also occur during pregnancy, usually after twenty weeks of pregnancy. This normally disappears after the baby has been delivered.

Eclampsia is a very serious complication although it is quite uncommon. It is usually a consequence of pre-eclampsia which is less serious ( it consists of persistent headaches, blurred vision and seeing spots, upper abdominal pain and sudden excessive lower leg swelling). Eclampsia can result in seizures and coma.

Fibroids are problems involving the uterus. They are growths that appear on the uterus but they are not always harmful but if it occurs during the second trimester, it could cause to a miscarriage which is also called spontaneous abortion (SAB). A miscarriage is the most common type of pregnancy loss. Fibroids are more likely to take place in older woman.

There are other possible complications that may take place during pregnancy but the most important thing for a mother to be to do is to get regular check ups to ensure that she is in good health.

What is childbirth?

Childbirth is the step that follows the period of nine months or 42 weeks of pregnancy, when the developed fetus or baby is pushed out of the mother's uterus and into the outside world, along the birth canal. It refers therefore exclusively to the vaginal delivery. It happens normally spontaneously after the period of gestation, but if the pregnancy goes past 42 weeks, it could be stimulated artificially. Childbirth is actually a whole process that includes two main phases: labor and delivery. The latter are themselves divided into different stages.

How does childbirth occur?

To answer this question, the main phases which are labor and delivery are to be developed:

Labor is the whole process of birth occurring before the birth itself, which is called the delivery.

Labor usually begins after the breaking of the bag of waters: it breaks under the pressure of the baby going towards the cervix, and lets the amniotic fluid flows away the uterus (see the section "What are the functions of the bag of waters?"). Labor can last from few hours to 24 hours, and even more; it is in this phase that the mother feels intense pain because she is undergoing contractions. These are due to the periodic tightening and relaxing of the uterus, because it is getting ready to deliver the baby. As the delivery time approaches, the contractions intensify. Eventually the baby is expelled followed by the delivery of the placenta. To describe these phenomenons in detail, it is necessary to mention that the process of labor and delivery is in fact divided into three stages:

First stage Dilation of the cervix (neck of the uterus that ends in the vagina) is the main part of this stage and the longest one, which is accompanied by contractions, and which lasts for about 14 hours during a first pregnancy, and for about eight hours during subsequent ones. This stage is divided into two phases, one is the latent (or early) labor, and the other one the active labor.

During the latent labor, that occurs first, the cervix opens or dilates to a width of about 4 centimeters, whereas at the end of the first stage it will open until 10 centimeters. While the cervix dilates progressively and slowly, the smooth muscles in the wall of the upper part of the uterus contract and thicken in order to expel the baby, causing periodic contractions, approximatively 30 seconds each at the beginning, and every ten minutes; the tightening of the muscles are stimulated by a hormone called ocytocin that the pituitary gland of the mother secrets increasingly in late pregnancy.

The pain the mother feels at these moments are tend to be mild, sometimes painless, but sometimes very painful too and the cervix may take a lot of time to dilate. Latent labor lasts from 6 to 12 hours, which is longer than the active labor because the process is slower. The mother is then encouraged to walk around, since it naturally stimulates the process, and she generally feels comfortable at this step.

Gradually the contractions become stronger, longer (40 to 60 seconds)and closer, i.e. the pauses between the periods of pain are shorter, then the cervix accelerates to dilate when its width reaches approximatively 4 centimeters: it is the beginning of the active labor, and indeed things go much faster in this phase. Within about 8 hours, the cervix opens from 4 to 10 centimeters, and as it has been said, the contractions appear more frequently with considerable pain. The cause is that the upper muscles really start to push down the baby by contracting firmly.

At this stage, the mother is advised to relax and to use some breathing exercises to bear the pain; alternatively, if asked, the doctor can give her medication or anesthetics.

When the cervix reaches an opening width of 8 centimeters and is on the way to 10 centimeters, a phase called the transition takes place, relating the first to the second stage of labor. That is the period of the most intense pain and of full dilation of the cervix. The head of the baby has already descended along the cervix and starts entering in the vagina, making the mother feel an urge to push with her abdominal muscles.

see Annex Pregnancy_Childbirth 5

Second stage

The period from full dilation of the cervix to delivery of the infant is called the expulsion stage. Strong uterine contractions, lasting about 1 minute each, occur every 2-3 minutes, and the mother feels an increasing urge to push with her abdominal muscles. Both the mother and the uterus work on the expulsion of the baby, one by pushing and the other one by contracting more and more. Within a period of 20 minutes to an hour or so, which is much less than the first stage, the infant is forced down and out of the uterus and vagina, either progressively while a first pregnancy or rapidly.

The head emerges first facing the back of the mother, immediately the doctor and the midwife will suction the mucus from the nose and the mouth in order to let it breathe, then the baby rotates to the side so that the shoulders are in position to get out, followed at last by the rest of the body. Then a midwife cuts the umbilical cord after the baby has been delivered. The end of the cord remains for several weeks, then it dries out and falls off, leaving the belly button.

see Annex Pregnancy_Childbirth 6

The third and final stage

The final stage is the delivery of the placenta ("afterbirth"), usually within 15 minutes after the birth of the baby. Once again the uterus will contract to separate the placenta from the uterine wall, and a gentle push is enough to deliver it without any pain. It takes only 5 to 10 minutes.

see Annex Pregnancy_Childbirth 7

Hormones continue to be important after the baby and placenta are delivered. But this state will vanish and the uterus will return to its prepregnancy state after some times; it is the result of the release of oxytocin after delivery. The mother also starts to produce and secrete milk by the mammary glands in order to give nutrients and antibodies to the baby that will help protect the infant from infection.

How and why is labor sometimes induced?

The labor phase is sometimes induced, it is what we call "labor induction" and it means that labor is stimulated artificially or naturally, because in most cases the pregnancy has gone two weeks or more past the due date. The problem may be that the baby grows too big inside the mother's body and she isn't able to carry it anymore; in addition, she won't have a sufficient food supply for the baby from inside her. Other reasons could be that:

The waters bag has broken but the mother doesn't have any contractions;
The mother has diabetes;
She has high blood pressure;
She has an infection in her uterus;
There isn't enough amniotic fluid around the baby in the uterus.
Both the baby and the mother have sever health problems.

Labor can be induced artificially or by natural ways.

How to Induce Labor artificially

There are a few different ways the labor can be medically induced. One common way is to use prostaglandin gel. This gel, which helps to soften the cervix, is applied to the back of the vagina. The gel alone may be enough to start labor, but it can also increase the risk of developing a fever, having diarrhea, cause fetal distress and possibly cause hemorrhage after birth.

Something with a bit less risk associated with it is having the water broken. However, to do this, the cervix needs to be dilated a few centimeters. Plus, some women find the procedure, which involves an instrument that resembles a large crochet hook, to be rather uncomfortable. While breaking the water can sometimes be enough to get labor going.

Another way may be an injection of oxytocin, a hormone that will start the contractions and help them to get strong and regular. Therefore tightening of the uterus and dilation of the cervix are induced.

Medical induction might take 2 or 3 days to work, however if it is a woman's first pregnancy it can take more time, and only then the mother is ready to deliver vaginally. There are some risks, such as the ineffectiveness of the medicine or the "over" effeciency, i.e. the contractions become too strong obliging the mother to take pain medications. In both cases the doctor could stop the procedure and decide on doing a cesarean section.

Natural Ways to Induce Labor

There are a number of home remedies for inducing labor naturally when the due date has past. But none of these remedies will start labor unless the vagina has already begun to dilate. However, some methods can help to tonify and soften the uterus.

Eat spicy food or pineapple.
Go for a walk or march up some stairs. This is a way to bring on labor because of the pressure of the baby's head pressing down on the cervix. At the very least, walking can help get the baby into a better position for labor.
Have sex. Sex can help by releasing a hormone, which causes the uterus to contract. Additionally, semen contains a substance, which will help soften the cervix.
Nipple stimulation. For women who find sex uncomfortable in their actual state of pregnancy, breast stimulation may be a better choice. It helps to bring on labor in much the same way sex does. However, this method may take a bit more effort to start labor.
Stretching of the uterine opening membranes. This can be done by the doctor or midwife and has been found to increase the chances of labor starting within 48 hours.
Complementary therapies. Acupuncture, massage, teas, herbs and homeopathic remedies can be helpful when it comes to inducing labor.

What are the functions of the waters bag?

First of all "bag of waters" is the popular name for amniotic sac with the amniotic fluid that it contains. It is formed in the uterus during pregnancy in which the fetus "bathes". The burst of this bag, known as "breaking the waters bag", happens just before labor, it in fact is the sign for the delivery time, because the contraction of the uterine wall causes it by pushing everything in the uterus down, and which is the beginning of labor. This fluid contains mostly water and urine of the mother; other components are nutrients, disfighting antibodies and hormones.

The bag of waters is very important to baby's health as its fluid protects it from shock and gives it space to move around, promoting the development of muscles and bones. Moreover, forming a sort of barrier, it protects from vaginal infections the mother may have. That's why it is better to induce labor if the waters has broken but the contractions hasn't start; the risk that an infection reaches the baby becomes higher. By the second trimester of pregnancy, the baby is able to breathe the amniotic fluid and to swallow it, which leads to normal growth and development of the lungs and intestinal system.

The liquid is clear, transparent, maybe a little yellowish, and without any smell; but if green, or pink, or brown or smelly then it indicates the baby has gone through health problems. In this case the mother should call the doctor right away.

What are the possible complications during childbirth?

Failure to Progress (Prolonged labor)

As we have said before, there are three stages of labor. The first stage is defined as the onset of labor to full dilation of the cervix. This is followed by the second stage, from full dilation to delivery, and the third stage begins after delivery of the infant and ends with delivery of the placenta. The average labor is from 12 to 18 hours. We say that the progress of labor is abnormal when the mother is having trouble dilating during the first stage, and when it takes more then 20 hours. The main cause to a prolonged labor, is an unusually big size of the fetus, which is too large to fit easily through the mother's pelvis. The other main cause, is an unusual position of the fetus, which makes the uterine contractions too week. There are of course some risks to a prolonged labor. And the longer it is, the higher the risk is. It could firstable provoke bleeding, due to the uterine muscles becoming tired, which can result in a post-partum hemorrhage. The mother needing to have a Cesarean delivery. The danger to the baby, is the fetal hypoxia. It means that the baby isn't getting enough oxygen and it can lead to a cardiac distress. However, this are very rare eventualities. Generally, even in a prolonged labor, there is no effects at all.

Abnormal Presentation

Presentation refers to the position the baby takes just before the delivery; the "normal" position should be what we call vertex presentation, it means the head, and more precisely the back of the head, will enter first into the mother's pelvis, facing her back. It is the ideal position since the head is the largest and the most solid part of the body, that way it will gently emerge and enlarge the cervix so that the body gets out then easily.

However as the fetus moves a lot during late pregnancy, it may take an abnormal position: either the buttocks or the feet of the baby are down-faced toward the cervix, a malpresentation called breech presentation. The risk in this case is that, the body being expelled first, the cervix and the birth canal may not be quite open and in consequence the head could get hung up.

There is another abnormal position called cephalic posterior or occiput presentation, where the head faces the mother's abdomen instead of her back. When the face will enter the birth canal, it may cause "back labor" or the tearing of the birth canal.

When a baby lies horizontally in the uterus, we say it presents in a transverse lie. The shoulders will lead here the way through the birth canal, increasing the chance of injuring or rupturing the uterus.

What happens when the head of the baby is too big?

In some cases the head of the baby is too large to go through the cervix, we call it cephalopelvic disproportion, thus the doctor proceeds either to a cesarean section or to an intervention called episiotomy. It consists in cutting up the skin of the perineum stretching from the vagina until the anus, in order to enlarge the vaginal opening so that the expulsion becomes easier.

Umbilical Cord Prolapse

The umbilical cord provides nutrients and oxygen to the baby, thus it is important that it has a free space and isn't oppressed. In a complication such as an umbilical cord prolapse, the latter precedes the baby in the birth canal and even sticks out the vagina, and as it enters in a narrow way, it can get blocked and stop the blood flow which quite dangerous.

Umbilical Cord Compression

It is nearly the same case as the last one, the only difference is that the cord get twisted around the baby because it moves a lot and so the cord gets compressed: the blood flow decreases, the baby's heartbeat therefore may decelerate. It isn't a major problem since it can be picked up by monitors during labor.

What is a cesarean section?

A cesarean section is a surgical intervention in which the abdomen and the uterus of the mother are incised (=cut) to deliver her baby, when she isn't having a vaginal delivery. Here are some reasons why women have to pass through c-section (abbreviation for cesarean section):

Umbilical cord prolapse
Placenta abruptio, where the placenta separates from the uterine wall before birth, or placenta previa, where it covers the cervix.
Abnormal presentations (see chapter "what are the possible complications during childbirth?")
Cephalopelvic disproportion
Mother's health conditions
Excessive pain during labor or prolonged labor making the mother exhausted and weak
Repeated cesarean, because if a woman had a c-section before, the incised region becomes fragile and the scar could rupture during a subsequent vaginal delivery (it is the most common reason)
Fetal distress, when the baby has an abnormal heartbeat.

Description

First the mother is anesthetized either locally, which is preferred, or in the spinal cord (spinal anesthesia), or in the epidural space (epidural anesthesia). In an emergency case however a general one is made because faster. Then the abdomen is washed with antibacterial solution and if needed a part of pubic hair is shaved. The first incision cuts the abdomen just above the pubic bone; usually horizontal incisions are made because it favors later vaginal delivery and less bleeding, but as the vertical ones provide a larger opening, this method is also used. The second incision opens the uterus and then the waters bag is ruptured, finally the baby is taken out by hand. The umbilical cord is cut, the placenta removed and the uterus is stitched followed by the abdomen.

see Annex Pregnancy_Childbirth 8

The whole operation lasts for about 30 to 40 minutes.

The mother has to spend three days or more for recovery, and it is suggested to rest for six weeks when she's back home, just like after a major surgery.