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Fetal development: What happens during the third trimester?
The countdown is on! See how fetal development continues as your due date approaches.
By Mayo Clinic staffThe end is in sight! By now, you may be tired of being pregnant — and eager to meet your baby face to face. But your uterus is still a busy place. See how fetal development continues as your due date approaches.
Week 28: Baby's eyes open
Your baby is about 15 inches long and weighs about 2 to 3 pounds.
Your baby's eyes are beginning to open and close. The color has been established, but the story's not over yet. Eye color may change within the first six months after birth — especially if your baby's eyes are blue or gray-blue at birth.
Your baby is now sleeping for about 20 to 30 minutes at a time. Fetal movement will be most obvious when you're sitting or lying down.
Week 29: Movement is more forceful
Your baby's bones are fully developed, but they're still soft and pliable. This week, your baby begins storing iron, calcium and phosphorus.
As your baby continues to grow, his or her movements will become more frequent and vigorous. Some of your baby's jabs and punches may even take your breath away.
Week 30: Baby packs on pounds
Your baby weighs about 3 pounds — but not for long. He or she will gain about 1/2 pound a week until week 37.
Your baby may practice breathing by moving his or her diaphragm in a repeating rhythm. If your baby gets the hiccups, you may feel slight twitches or spasms in your uterus.
Week 31: Reproductive development continues
If your baby is a boy, his testicles are moving from their location near the kidneys through the groin on their way into the scrotum. If your baby is a girl, her clitoris is now relatively prominent.
Your baby's lungs are more developed, but they're not fully mature. If your baby is born this week, he or she will probably need a ventilator to assist breathing. Complications such as bleeding in the brain are less likely than they were even a few weeks ago.
Week 32: Downy hair falls off
Your baby is between 15 and 17 inches long and weighs about 4 to 4 1/2 pounds. Nearly all babies born at this age survive the challenges of premature birth.
The layer of soft, downy hair that has covered your baby's skin for the past few months — known as lanugo — starts to fall off this week.
As space in your uterus becomes more cramped, your baby's kicks and other movements may seem less forceful. You may want to check on your baby's movements from time to time — especially if you think you've noticed decreased activity. If you count fewer than 10 movements in two hours, contact your health care provider.
Week 33: Baby detects light
Your baby's pupils now constrict, dilate and detect light. Your baby continues to gain about 1/2 pound a week, and his or her lungs are more completely developed. Babies born this week need extra attention, but almost all will be healthy.
Week 34: Protective coating gets thicker
The pasty white coating that protects your baby's skin — called vernix — gets thicker this week. When your baby is born, you may see traces of vernix firsthand, especially under the arms, behind the ears and in the groin area. The soft, downy hair that covered your baby under the vernix for the past few months is now almost completely gone.
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