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Beginnings: Pregnancy, Birth & Beyond

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Third trimester: Your growing baby

The third trimester is a time of steady growth as your baby matures and gets ready for birth. As your baby gains weight, fat is stored under the skin. This smoothes your baby's skin and makes your baby look plumper.

During the beginning of this trimester, you may feel plenty of kicks, squirms, flips, hiccups, and other movements in between quiet periods. Your baby starts having regular sleep and wake cycles, and you will notice the difference in activity. You may also notice your baby responding to bright light as well as sound.

Important

Although many people consider pregnancy to last nine months, it is actually 280 days, measured from the first day of the last menstrual period, or 40 weeks. The "due date" is day 280 or the end of the 40th week.

By the 28th week your baby has eyelashes, and his hair is growing. His fingernails have grown to the end of his fingertips. The lanugo, the downy hair, is beginning to disappear.

This is also the start of dramatic brain growth that will continue for your baby's first two years.

Your baby's lungs are beginning to reach maturity, meaning your baby would have a good chance of surviving if born now. Your baby is about two pounds and is about 13 inches from crown to rump.

At 32 weeks your baby has grown so much that there is much less room to move around. You can feel the difference in your baby's movements, which are more like wriggling and twisting.

Your baby may settle into a favorite position. That can make it easier to identify his feet, elbows and hands when these push against the wall of your uterus. The vernix coating on your baby's skin is beginning to be absorbed.

Starting in week 36, your baby gains about half a pound and grows half an inch a week. Many babies turn headdown and stay in that position for birth. First babies are likely to settle into the mother's pelvis at about week 38.

This act of the head engaging in the pelvis is called lightening. It makes your breathing easier but creates pelvic pressure. If this is not your first baby, your baby's head may not engage until you go into labor.

After week 37, your baby is considered "term," which means fully-grown. Term babies often weigh 7 to 8 pounds and are 18 to 21 inches long, measuring from top of the head to the feet.

Baby's development: Weeks 27 to 40

 

Week 27

Baby's hair is longer.
Eyelashes and eyebrows are very noticeable.

Week 28

Illustration of baby at week 28Eyes are open and sensitive to light.
Baby is about 15 inches long and weighs about 3 pounds.

Week 29

Baby gains about 7 ounces a week.

Week 30

Taste buds develop.
All of baby's senses are developed.

Week 31

Vernix (a creamy coating on the skin) and lanugo (the fine hair that covers the baby's body) begin to disappear.
Baby's head is more in proportion to the body.

Week 32

Illustration of baby at week 32Skin is less wrinkled, but baby is still thin.
Baby is about 18 inches long and weighs about 5 pounds.

Week 33

Baby's movements can be seen on the outside of the mother's abdomen.

Week 34

Skin is becoming more pink.
Baby is blinking.

Week 35

Fingernails and toenails have grown to the end of baby's fingers and toes.

Week 36

Illustration of baby at week 36All organs are now mature.
Skin is red but smooth.
Baby is about 19 inches long and weighs about 6 pounds.

Week 37

Deposits of fat continue to form.
Baby is considered full-term.

Week 38

Baby gains 1 ounce a day.
Baby may move down into pelvic area.

Week 39

Fine hair remains only on arms and shoulders.
Fingernails are now beyond the ends of fingertips.

Week 40

Baby is fully developed.
Baby is about 20 inches long and weighs 7 to 8 pounds.


 

Source: Allina Health's Patient Education Department, Beginnings: Pregnancy, Birth and Beyond, sixth edition, preg-ahc-90026, ISBN 1-931876-25-8

First published: 10/04/2002
Last updated: 08/22/2011

Reviewed by: Allina Health's Patient Education Department experts