Mayo Clinic Guide to a Healthy Pregnancy: From Doctors Who Are Parents, Too!

CHAPTER 13. Month 10: Weeks 37 to 40

I think nature’s way of making us look forward to labor is to make the final month so uncomfortable. I can handle a few more weeks, but I’m definitely ready to have this child. — Kris

Month 10! Pregnancy is only supposed to be nine months! What’s going on? In case you missed it, in our introduction to Part 2 we explain why this book is divided into 10 months instead of nine. Birth can happen at any time now. However, pregnancy is officially considered complete at 40 weeks.


In these final weeks, your uterus finishes expanding and baby gets plump. During the final weeks, weight gain varies, depending on the child. Some babies put on more weight than do others.

Week 37 By the end of this week, your baby is considered full-term. He or she isn’t quite done growing yet, but the rate of weight gain has slowed. As fat is being laid down, your baby’s body is slowly becoming rounder. A baby’s gender seems to play some role in determining size at birth. If you have a boy, he’ll likely weigh a bit more than a baby girl born to you at a similar length of gestation.

Week 38 In recent weeks, your baby’s development has focused mainly on improving organ functioning. Your baby’s brain and nervous system are working better every day. However, this developmental process continues through childhood and even into the later teen years. This month, your baby’s brain has prepared to manage the complicated jobs of breathing, digesting, eating and maintaining a proper heart rate.

At 38 weeks into pregnancy, the average baby weighs about 6 pounds, 13 ounces and is about 14 inches long, crown to rump.

Week 39 Baby has now lost most of the vernix and lanugo that used to cover his or her skin, although you may see traces of them at birth. Your baby now has enough fat laid down under the skin to hold his or her body temperature as long as there’s a little help from you. This fat gives baby the familiar healthy, chubby look seen at birth.

Even though the rest of the body has been catching up, baby’s head is still the largest part of his or her body, and that’s why it’s ideal when babies are born headfirst.

You continue to supply your baby with antibodies, protein substances that help protect against bacteria and viruses. The antibodies cross the placenta from you to your baby. During the first six months of your baby’s life, these antibodies help your baby’s immune system stave off infections. Some of these antibodies also are provided through breast milk.

By the 39th week of pregnancy, the average baby weighs about 7 to 7½ pounds. By now individual differences in babies become noticeable. A 39-week-old baby may weigh from 6 to 9 pounds.

Week 40 Your due date arrives this week. Yippee! However, only about 5 percent of women deliver on their due dates. It’s just as normal to have your baby a week late as it is to have him or her a week early. Try to be patient, although with all the work you’ve done, that’s not easy!

As labor approaches, your baby will experience many changes in order to prepare for birth, including a surge in hormones. This may help maintain blood pressure and blood sugar levels after birth. It may also have something to do with communicating to your uterus that the time has come.

With labor, your baby is prepared for the blood flow to the placenta to decrease a bit with each contraction. Your baby can coast through these interruptions so long as they aren’t too frequent and don’t last too long. The changes your baby will experience at birth are truly amazing. All that has gone before is prologue to this wonderful, glorious event.

At 40 weeks, the average baby weighs about 7 to 8 pounds and measures about 18 to 20½ inches long with legs fully extended. Your own baby may be smaller or larger and still be normal and healthy.


Before you were pregnant, your uterus weighed only about 2 ounces and could hold less than a half-ounce. At term, it will have multiplied in weight by a factor of 20, to about 2½ pounds and will have stretched to hold your baby, your placenta and about a quart of amniotic fluid.

What’s happening and where At the end of this month, after 40 weeks of growth and change, you’ll go through labor and delivery, giving birth to a new human being — a unique, one-of-a-kind boy or girl.

Respiratory system You may still experience shortness of breath. If your baby drops lower into your pelvis before labor begins, which is more common among first-time moms, you may feel less pressure on your diaphragm. However, many women experience shortness of breath throughout pregnancy because as baby grows, it exerts pressure under the ribcage.

Digestive system As it has for the past several months, your digestive system continues to operate at a slowed pace. You may still experience heartburn and constipation. If your baby drops this month, these symptoms may improve. With less pressure on your stomach, digestion may be easier.

Breasts Stimulated by the hormones estrogen and progesterone, your breasts are fully prepared to feed your baby. As delivery approaches, your nipples may start leaking colostrum — the yellowish protein fluid your breasts first produce.

Over the course of pregnancy, some womens’ nipples become inverted, dimpling back into their breasts. If this happens to you, don’t worry. A lactation consultant can help prepare your nipples for breast-feeding.

Uterus This month, your uterus will complete its expansion. When you reach term, it will extend from your pubic area to the bottom of your rib cage. If this is your first baby, the baby may drop lower into your pelvis (lightening) weeks before you go into labor. If you’ve been through childbirth before, lightening and the onset of labor tend to happen closer together.

Urinary tract You may find it difficult to get a good night’s sleep because you have to get up so often to urinate. You’re probably also continuing to leak urine, especially when you laugh, cough or sneeze. Hang in there. Your pregnancy is almost over.

Bones, muscles and joints The aptly named hormone relaxin, which is produced by your placenta, continues to relax and loosen the ligaments holding your three pelvic bones together. This will allow your pelvis to open wider during childbirth — wide enough to accommodate your baby’s head as it passes through. For now, the effects of relaxin manifest themselves in clumsiness and loose-feeling limbs.

If your baby drops a couple of weeks before labor begins, which is more common among first-time moms, you may also feel some pressure or aches and pains in your pelvic joints.

Vagina At some point over the next several weeks, your cervix will begin to open (dilate). It may start a couple of weeks before labor begins, or just a few hours. Ultimately, your cervical opening will stretch from 0 to 10 centimeters in diameter so that you can push your baby out. As your cervix dilates, you may feel an occasional sharp, stabbing pain inside your vagina. You may also feel pressure, aches or sharp twinges in your perineal area — the area between your vaginal opening and anus — as your baby’s head presses on your pelvic floor.

As the cervix thins and relaxes, you may lose the mucous plug that’s been blocking your cervical opening during your pregnancy to keep bacteria from getting into your uterus. There isn’t a strong relationship between the loss of the mucous plug and the beginning of labor. It can happen up to two weeks before labor begins — or it can happen right before. When it happens, you may notice a thick discharge or stringy mucus that’s clear, pink or blood tinged. Don’t worry if you don’t notice this change. Some women don’t even realize it when they’ve lost their mucous plug.

Among a few pregnant women, the amniotic sac breaks or leaks before labor begins, and the fluid that has cushioned the baby comes out as a trickle or a gush. If this happens to you, follow your care provider’s instructions. He or she will probably want to evaluate you and your baby as soon as your water breaks (membranes rupture). In the meantime, don’t do anything that could introduce bacteria into your vagina. That means don’t use tampons for any reason or have sexual intercourse.

If the fluid coming from your vagina is anything other than clear and colorless, let your care provider know right away. For example, vaginal fluid that’s greenish or yellowish and foul smelling could be a sign of a uterine infection or that your baby has passed a bit of stool into the fluid.

Weight gain Your baby is actually gaining weight more slowly this month. As a result, you may notice that your own weight gain has slowed or even stopped. Some women even lose a pound or so at the very end of the pregnancy. By the time you reach your due date, you’ll probably have gained roughly 25 to 35 pounds.


By this point, you’re likely tired of being pregnant. You may be having trouble sleeping because you can’t find a comfortable position. Once you do drift off, your bladder may be waking you up every couple of hours. Time may seem to be standing still.

To deal with the boredom and discomfort, try to keep busy. Find a project to work on, read the latest best-seller, and spend time with friends and family. Keeping your mind active will help the days move more quickly until the big day finally arrives and you’re in labor. Plus, who knows when you’ll have so much time to yourself again?


It’s a fact: If you’re frightened and anxious during labor, you’ll have a more difficult labor. Stress sets in motion a whole range of reactions in your body that can ultimately interfere with labor. Childbirth educators call it the fear-tension-pain cycle. To keep yourself from becoming too stressed, you need to find ways to relax. There are many ways you can do this. The right music can be soothing. So can a cool evening breeze or an evening with your feet up watching a funny movie.

Techniques to keep you calm There are also different relaxation techniques that you can use to help you keep calm. Progressive muscle relaxation, touch relaxation, massage and guided imagery are just some of the options. You may have learned about these techniques in your childbirth course, but here’s a quick refresher:

 Progressive muscle relaxation. Beginning with your head or feet, relax one muscle group at a time, moving toward the opposite end of your body.

 Touch relaxation. Starting at your temples, have your partner apply firm but gentle pressure for several seconds. Then move to the base of your skull, shoulders, back, arms, hands, legs and feet. As your partner touches each part of your body, relax the muscle group in that area.

 Massage. Your partner massages your back and shoulders, making sweeping motions down your arms and legs and small circular motions on your brow and temples. These movements will help relax your muscles and cause your brain to release endorphins, chemicals that help enhance your sense of well-being. Experiment with different techniques until you find a form of massage that feels good to you.

 Guided imagery. Imagine yourself in an environment that gives you a feeling of relaxation and well-being — that special, peaceful place you go to in your imagination. Concentrate on the details, such as the smells, colors or sensations on your skin. To help enhance the imagery, play a nature tape or soft music.

 Meditation. With this mind and body technique, you focus your attention on your breathing or on repeating a word, phrase or sound. This is done in order to interrupt the stream of thoughts that normally occupies the conscious mind. When your normal thoughts are suspended, you enter a state of physical relaxation and mental calmness.

 Breathing techniques. Inhale through your nose, envisioning cool, pure air rushing into your lungs. Exhale slowly through your mouth, imagining yourself blowing all your tension away. Practice breathing both more slowly and more quickly than normal. You can use both these techniques, and others, during labor.

Practice relaxation techniques often this month. When you do, make sure the environment is peaceful and that you’re comfortable. Use pillows if you want, or turn on some soft music.


You’ll likely see your care provider weekly now until baby arrives. Don’t be surprised if your provider performs one or more pelvic exams. This exam can help him or her confirm how your baby is positioned: headfirst, feet-first or rump-first inside your uterus. Most babies are positioned headfirst. As your due date draws closer, your care provider may use the terms station and presenting part. Presenting part is the medical term for the part of your baby’s body that’s farthest down in your pelvis. Station refers to how far down in your pelvis the presenting part is.

During your pelvic exams, your care provider may also check your cervix to see how much it has begun to soften, as well as how much it has opened (dilated) and thinned (effaced). This information will come across in numbers and percentages. For example, your care provider may tell you that you’re 3 centimeters (cm) dilated and 30 percent effaced. When you’re ready to push your baby out, your cervix will be 10 cm dilated and 100 percent effaced.

Don’t put too much stock in these numbers. You may go for weeks dilated at 3 cm, or you may go into labor without any dilation or effacement at all beforehand. However, measures of your cervix do let your care provider know if induction of labor is likely to proceed should you need to be induced.

When to call During the last month of pregnancy, these signs and symptoms require immediate medical attention:

Vaginal bleeding If you have bright red bleeding of more than a spot or two at any time this month, call your care provider right away. It could be a sign of placental abruption, a serious problem in which your placenta separates from the wall of your uterus. This condition is a medical emergency. Don’t confuse this kind of bleeding with the slight bleeding you may have after a pelvic exam or with bloody show.

Constant, severe abdominal pain If you have constant, severe abdominal pain, contact your care provider immediately. Although uncommon, this can be another sign of placental abruption. If, in addition to pain, you also have a fever and vaginal discharge, you may have an infection.

Decreased movement It’s normal for the vigor of your baby’s activities to decrease somewhat during the last few days before birth. It’s almost as if your baby is resting and storing up energy for the big day. But the number of movements shouldn’t drop a great deal. Decreased frequency of movement may be a signal that something is wrong. To check your baby’s movements, lie on your left side and count how often you feel the baby move. If you notice fewer than 4 movements per hour or if you’re otherwise worried about your baby’s decreased movement, call your care provider.

What to do when baby’s overdue Your due date has come and gone — and you’re still pregnant. What’s going on? Although your due date may seem to have magical qualities, it’s simply an educated guess about when your baby is most likely to arrive. It’s perfectly normal to give birth one to two weeks before — or after — your due date. In fact, your pregnancy must continue two weeks past your due date to earn the official label of overdue pregnancy, also known as post-term pregnancy.

You may be more likely to have an overdue pregnancy if:

 The exact date of the start of your last menstrual period isn’t known, in which your due date may be wrong

 This is your first pregnancy

 You’ve had previous overdue pregnancies

 Overdue pregnancies tend to run in your family

 Your baby is a boy

Rarely, an overdue pregnancy may be related to problems with the placenta or the baby.

You will continue your prenatal visits if your pregnancy extends beyond your due date, and your care provider will continue to monitor your health. He or she will also check your cervix to see if it’s begun to thin and dilate in preparation for labor. If you’re more than one week past your due date, your care provider may track your baby’s heartbeat with an electronic fetal monitor or use ultrasound to observe your baby’s movements and to measure the amount of amniotic fluid.

Giving baby a nudge Sometimes it’s better to deliver your baby sooner rather than later — particularly if your care provider is concerned about your health or your baby’s health or if your pregnancy continues more than two weeks past your due date.

Why the concern about two weeks? At this point in your pregnancy, your baby’s size may complicate a vaginal delivery. In a few cases, aging of the placenta can compromise a baby’s ability to thrive in the womb. An overdue baby is also more likely to inhale fecal waste (meconium), which can cause breathing problems or an infection after birth.

If you are overdue, your care provider may recommend inducing labor — taking steps to try and kick-start your labor. You may be given medication to help your cervix soften and open. If your amniotic sac is still intact, your care provider may break your water by creating an opening in the sac with a thin plastic hook. The process doesn’t hurt, but you may feel a warm gush of fluid when the sac breaks open.

If necessary, you may also be given medication to promote contractions. A common choice is Pitocin, a synthetic version of the hormone oxytocin, which causes the uterus to contract. The dosage may be adjusted to regulate the strength and frequency of your contractions.

For more information on handling an overdue pregnancy, see inducing labor in Chapter 28.