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Week 37
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How Big Is Your Baby?

Your baby weighs almost 6.5 pounds (2950g). Crown-to-rump length is 14 inches (35cm). Its total length is 21 inches (47cm).

How Big Are You?

Your uterus may stay the same size as measured in the last week or two. Measuring from the pubic symphysis, the top of the uterus is about 14.8 inches (37cm). From the bellybutton, it is 6.4 to 6.8 inches (16 to 17cm). Your weight gain by this time should be about as high as it will go at 25 to 35 pounds (11.2 to 13.5kg).

How Your Baby Is Growing and Developing

Is My Baby's Head Down in the Pelvis?

Your baby is continuing to grow and to gain weight, even during these last few weeks of pregnancy. As the illustration on page 309 shows, the baby's head is usually directed down into the pelvis around this time. However, in about 3% of all pregnancies, the baby's bottom or legs come into the pelvis first. Called a breech presentation, it is discussed in Week 38.

Maturation of Your Baby's Lungs and Respiratory System

A very important part of your baby's development is maturation of the lungs and respiratory system. When a baby is born prematurely, a common problem is development of respiratory-distress syndrome in the newborn fetus. This problem is also called hyaline membrane disease. In this situation, lungs are not completely mature, and the baby can't breathe on its own without help. Oxygen is necessary. The baby may require a machine, such as a ventilator, to breathe for it.

In the early 1970s, scientists developed a couple of methods for evaluating the maturity of fetal lungs. An amniocentesis test must be done at this point in pregnancy for either test. The first method, the L/S ratio, enables doctors to determine in advance if a baby can breathe on its own after delivery.

The L/S-ratio test doesn't usually indicate a baby's lungs are mature until at least 34 weeks of pregnancy. At that time, the relationship between two blood factors in the amniotic fluid changes. Levels of lecithin go up and levels of sphingomyelin go down. The ratio between these two levels indicates if a baby's lungs are mature.

The phosphatidyl glycerol (PG) test is another way doctors can evaluate the maturity of the baby's lungs. This test is either positive or negative. If phosphatidyl glycerol is present in the amniotic fluid (positive result), doctors are reassured; the infant will probably not suffer respiratory distress upon delivery.

Specific cells in the lungs produce chemicals that are essential for respiration immediately after birth. An important part of a newborn baby's breathing is determined by the chemical

surfactant. A baby born prematurely may not have surfactant in its lungs. Surfactant can be introduced directly into the lungs of the newborn to prevent respiratory-distress syndrome. The chemical is available for immediate use by the baby. Many premature babies who receive surfactant do not have to be put on respiratorsùthey can breathe on their own!

Changes in You

Pelvic Exam in Late Pregnancy

About this time in your pregnancy, your doctor may do a pelvic exam. This pelvic exam helps your doctor evaluate the progress of your pregnancy. One of the first things he or she will observe is whether you are leaking amniotic fluid. If you think you are, it's important to tell your doctor.

Your doctor will examine your cervix at the pelvic exam. During labor, the cervix usually becomes softer and thins out. This process is called effacement. Your doctor will evaluate the cervix for its softness or firmness and the amount of thinning.

Before labor begins, the cervix is thick and is ô0% effaced.ö When you're in active labor, the cervix thins out; when it is half-thinned, it is ô50% effaced.ö Immediately before delivery, the cervix is ô100% effacedö or ôcompletely effaced.ö

The dilatation (amount of opening) of the cervix is also important. This is usually measured in centimeters. The cervix is fully open when the diameter of the cervical opening measures 10cm. The goal is to be a 10! Before labor begins, the cervix may be closed. Or it may be open a little way, such as 1cm (0.4 inch). The goal of labor is the stretching and opening of the cervix so the baby fits through it and can pass out of the uterus.

Your doctor also evaluates whether the baby's head, bottom or legs are coming first. (He or she may refer to a ôpresenting part.ö) The shape of your pelvic bones is also noted.

The station is also determined. Station describes the degree to which the presenting part of the baby has descended into the birth canal. If the baby's head is at a -2 station, it means the head is higher inside you than if it were at a +2 station. The 0 point is a bony landmark in the pelvis, the starting place of the birth canal.

Think of the birth canal as a tube going from the pelvic girdle down through the pelvis and out the vagina. The baby travels through this tube from the uterus. It's possible that you may dilate during labor but the baby doesn't move down through the pelvis. In this case, a C-section may be called for because the baby's head doesn't fit through the pelvic girdle.

What Can Your Doctor Tell from a Pelvic Exam?

When your doctor examines you, he or she may describe your situation in medical terms. You might hear you are ô2cm, 50% and a -2 station.ö This means the cervix is open 2cm (about 1 inch), it is halfway thinned out (50% effaced) and the presenting part (baby's head, feet or buttocks) is at a -2 station.

Try to remember this information. It's helpful information when you go to the hospital and are checked there by a nurse or doctor. You can tell the medical personnel in labor and delivery what your dilatation and effacement were at your last checkup so they can know if your situation has changed.

How Your Actions Affect Your Baby's Development

Choosing Your Baby's Doctor

At this point in your pregnancy, it's time to choose a doctor for your baby. You might choose a pediatricianùa doctor who specializes in treating children. Or you might choose a family practitioner. If the doctor you are seeing during pregnancy is a family practitioner, and you want him or her to care for your baby, you probably don't need to consider this at all.

It's good to meet this doctor before the birth of your baby. Many pediatricians welcome it. This gives you the opportunity to discuss matters that are important to you with this new caregiver. You might want to talk to him or her about a circumcision for your baby if it's a boy. You may want to ask questions about breastfeeding, exams, inoculations and vaccinations, emergencies and other things that concern you. It's also good to find out whether a particular doctor shares your views on child rearing.

By choosing someone to care for your baby before it's born, you have a chance to take part in deciding who will have that important task. If you don't, the doctor who delivers your baby or hospital personnel will select someone. Another good reason for choosing someone ahead of time is if your baby has complications.

After your baby is born, the pediatrician will visit him or her in the hospital and give the baby a physical exam within 24 hours after birth. Then he or she will visit you in the hospital, let you know how things are going for the baby and arrange for follow-up care after you leave the hospital.

Preregistering at the Hospital

During pregnancy, your doctor has recorded various things that have occurred during your pregnancy. A copy of this record is usually kept in the labor-and-delivery area.

It may be very helpful and save you time if you register at the hospital a few weeks before your due date. You will be able to do this with forms that you get at your doctor's office or by getting forms from the hospital. It's wise to do this before you go to the hospital in labor because by then you may be in a hurry or concerned with other things.

You should know certain facts that may not be included in your chart. It's helpful to know your blood type and Rh-factor. You should be able to say when your last period was and when your due date is. Be able to describe other pregnancies or complications with other pregnancies. Know your doctor's name and your pediatrician's name.

Will You Have an Enema?

Will you be required to have an enema when you arrive at labor and delivery? Most hospitals offer an enema at the beginning of labor, but it is not usually mandatory.

Paige didn't want an enema, but she decided to follow her friends' advice and have one. She told me after her delivery she was glad she did. There are certain advantages to having an enema before labor. You may not want to have a bowel movement soon after your baby's delivery because of discomfort with an episiotomy. Having an enema before labor can prevent this discomfort.

An enema before labor can also make the birth of your baby a more pleasant experience. When the baby's head comes out through the birth canal, anything in the rectum comes out, too.

Discuss it with your doctor. Ask his or her opinion, and find out about the policy at the hospital you're going to.

You Should also Know

What Is Back Labor?

Some women experience back labor. Back labor refers to a baby that is coming out through the birth canal looking straight up. With this type of labor, you will probably experience lower-back pain.

The mechanics of labor work better if the baby is looking down at the ground so it can extend its head as it comes out through the birth canal. If the baby can't extend its head, its chin points toward its chest. This can cause pain in your lower back during labor.

This type of labor can last longer. Your doctor may need to rotate the baby's head so it comes out looking down at the ground rather than up at the sky.

How Is Your Baby Presenting?

At what point in your pregnancy can your doctor tell how baby is presenting for deliveryùfor example, if the baby's head is down or if you are carrying the baby breech? At what point will the baby stay in the position it is in?

Usually between 32 and 34 weeks of pregnancy, you can feel the baby's head in the lower abdomen below your umbilicus. Some women can feel different parts of the baby earlier than this. But the baby's head may not be hard enough yet to identify as the head.

The head gradually becomes harder as calcium is deposited in the fetal skull. Your baby's head has a distinct feeling. It is different from the feeling your doctor gets with a breech. A breech position has a soft, round feeling.

Beginning at 32 to 34 weeks, your doctor will probably feel your abdomen to determine how the baby is lying inside you. This position may have changed many times during pregnancy.

At 34 to 36 weeks of pregnancy, the baby usually gets into the position it's going to stay in. If you have a breech at 37 weeks, it's possible the baby can still turn to be head-down. But it becomes less likely the closer you get to the end of your pregnancy.

It may be difficult at times to tell the exact location of different parts of the baby. You may have a good idea according to where you feel kicks and punches. Ask your doctor to show you on your tummy how the baby is lying. Some doctors even take a pen and draw on your stomach to show you. You can leave it so you can show your partner how your baby was lying when you were seen in the office that day.

Will My Doctor Have to Use Forceps?

The use of forcepsùmetal instruments used in the delivery of babiesùhas decreased in recent years for a couple of reasons. One is the more frequent use of Cesarean delivery to deliver a baby that might be very high up in the pelvis. A C-section may be much safer for the baby if it's not very close to delivering on its own.

Another reason for the decrease in the use of forceps is the use of a vacuum extractor. There are two types of vacuum extractors. One has a plastic cup that fits on the baby's head by suction. The other has a metal cup. The doctor is able to pull on the vacuum cup to deliver the baby's head. The vacuum easily releases from the baby's head, so the baby can't be pulled as hard through the birth canal as with forceps.

The goal with every birth is to deliver the baby as safely as possible. If a large amount of traction with forceps is needed to deliver the baby, a Cesarean section might be a better choice.

If the possible use of a vacuum extractor or forceps causes you concern, discuss it with your physician. It's important to establish good communication with your doctor so you can communicate before and during labor about these concerns.

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From Your Pregnancy Week by Week by Glade B. Curtis, M.D., OB/GYN. Copyright by Fisher Books. Electronic rights by Medical Data Exchange.

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