Fetal development: The third trimester

Fetal development continues during the third trimester. Your baby will open his or her eyes, gain more weight, and prepare for delivery.

By Mayo Clinic staff

The end of your pregnancy is near! By now, you might be tired of being pregnant — and eager to meet your baby face to face. Your uterus, however, is still a busy place. Understand how fetal development continues as you approach your due date. Here's a weekly calendar of events for the third trimester. Keep in mind that measurements are approximate.

Week 28: Baby's eyes open

Twenty-eight weeks into your pregnancy, or 26 weeks after conception, your baby's eyelids are partially open and eyelashes have formed. Your baby is gaining weight, which is smoothing out many of the wrinkles in his or her skin.

By now your baby might be nearly 10 inches (250 millimeters) long from crown to rump and weigh nearly 2 1/4 pounds (1,000 grams). Otherwise healthy babies born this week have a 90 percent chance of survival without physical or neurological impairment — and the odds improve with each passing week.

Week 29: Baby's bones are fully developed

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Illustration of fetus 27 weeks after conception Fetal development 27 weeks after conception

Twenty-nine weeks into your pregnancy, or 27 weeks after conception, your baby's bones are fully developed, but they're still soft and pliable.

Week 30: Baby's eyes are wide open

Thirty weeks into your pregnancy, or 28 weeks after conception, your baby's eyes are wide open a good part of the time. Your baby might have a good head of hair by this week. Red blood cells are now forming in your baby's bone marrow.

By now your baby might be more than 10 1/2 inches (270 millimeters) long from crown to rump and weigh nearly 3 pounds (1,300 grams).

Week 31: Sexual development continues

Thirty-one weeks into your pregnancy, or 29 weeks after conception, your baby's central nervous system has matured to the stage where it can control body temperature.

Week 32: Baby practices breathing

Thirty-two weeks into your pregnancy, or 30 weeks after conception, your baby's toenails are visible.

Although your baby's lungs aren't fully formed, he or she practices breathing. Your baby's body begins absorbing vital minerals, such as iron and calcium from the intestinal tract. 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.

By now your baby might be 11 inches (280 millimeters) long from crown to rump and weigh 3 3/4 pounds (1,700 grams).

Week 33: Baby detects light

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Illustration of fetus 31 weeks after conception Fetal development 31 weeks after conception

Thirty-three weeks into your pregnancy, or 31 weeks after conception, your baby's pupils can constrict, dilate and detect light entering his or her eyes.

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References
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  5. Frequently asked questions. Pregnancy FAQ069. What to expect after your due date. The American Congress of Obstetricians and Gynecologists. http://www.acog.org/Resources_And_Publications/~/media/For%20Patients/faq069.ashx. Accessed Nov. 16, 2012.
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PR00114 Dec. 4, 2012

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