Your Baby’s Development: The Third Trimester

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When is the third trimester?

The third and final trimester is week 27 through the end of pregnancy.

By the end of the second trimester, all of your baby’s organs and body parts are present and working correctly. Now everything needs to grow and mature.

What does my baby feel during this trimester?

Your baby begins using the senses of hearing and touch to learn about his or her own body and your surrounding womb. The baby still can’t see much, though. While his or her eyes can detect very bright light, it’s too dark to see in the uterus.

Your baby can hear and recognize your voice and might move in response to music.

Your baby uses his or her sense of touch to practice important movements, including grasping and sucking, and he or she may start sucking on his or her thumb.

Will I still feel my baby move?

You’ll feel your baby kicking, punching and moving often in the early weeks of the third trimester. Later, as your baby gets larger, you’ll likely feel stretches and rolls, and fewer kicks and punches.

As your uterus gets more and more crowded, you may feel your baby moving less. If you think your baby is less active than usual, do a “kick count”—keep track of the number of movements in 1 hour. If your baby moves fewer than 10 times in an hour, call your doctor right away.

How big will my baby grow during the third trimester?

At birth, most babies weigh somewhere between 6 and 9 pounds. They’re usually between 19 and 21 inches long.

As your baby grows, he or she adds layers of fat to help provide warmth after birth. The fat also fills the extra space under the skin, making the skin less wrinkled.

Other highlights of the third trimester

  • By the end of the trimester, your baby has eyelashes and eyebrows and may have a full head of hair. Or, he or she may be born bald. Nails have grown to the tips of the fingers and toes.
  • The white waxy substance and fine hair that covered and protected your baby’s skin in the second trimester has begun to fall off. You may see some of the leftover hair after your baby is born. Most of this usually is gone within the first few weeks of life.
  • Most babies move to a head-down position in the uterus toward the end of the third trimester, with the head on the mother’s pubic bone.
  • The lungs are the last major organ to finish developing. When they’re fully mature, they produce a chemical that affects the hormones in your body. Doctors aren’t sure why labor starts, but this chemical may be one of the causes.

Will my baby be big enough to survive if he or she is born before my due date?

The due date is an estimate. Only 5 percent of babies are actually born on their due dates. Your baby is “full-term” (not premature) if he or she is born during or after the 37th week of pregnancy. If this is your first pregnancy, your baby is likely to be born after your due date.

Even if your baby is born near the beginning of the third trimester, he or she is likely to survive. However, the longer the baby remains in the womb, the healthier he or she will be.