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third trimester

31 Dec

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 may be tired of being pregnant — and eager to meet your baby face to face. But your uterus 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.

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 may 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

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. This week, your baby begins storing iron, calcium and phosphorus.

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. Your baby may have a good head of hair by this week.

By now your baby may 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 sexual development continues.

If your baby is a boy, his testicles are moving through the groin on their way into the scrotum. If your baby is a girl, her clitoris is now relatively prominent.

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. 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. Your baby’s kicks and jabs may be forceful.

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

Week 33: Baby detects light

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.

Week 34: Baby’s fingernails grow

Thirty-four weeks into your pregnancy, or 32 weeks after conception, your baby’s fingernails have reached his or her fingertips.

By now your baby may be nearly 1 foot (300 millimeters) long from crown to rump and weigh more than 4 1/2 pounds (2,100 grams).

Week 35: Protective coating thickens

Thirty-five weeks into your pregnancy, or 33 weeks after conception, your baby’s body has become round. The pasty white coating that protects your baby’s skin — the vernix caseosa — is getting thicker.

Week 36: Rapid weight gain begins

Thirty-six weeks into your pregnancy, or 34 weeks after conception, your baby is gaining weight rapidly — about 1/2 pound (227 grams) a week for the next month.

The crowded conditions inside your uterus may make it harder for your baby to give you a punch, but you’ll probably feel lots of stretches, rolls and wiggles. You may want to check on your baby’s movements from time to time — especially if you think you’ve noticed decreased activity. Ask your health care provider how many movements you should detect in a certain number of hours.

Week 37: Baby is full-term

Thirty-seven weeks into your pregnancy, or 35 weeks after conception, your baby will be considered full-term. Your baby’s organs are ready to function on their own. To prepare for birth, your baby may descend into the head-down position.

Week 38: Baby develops a firm grasp

Thirty-eight weeks into your pregnancy, or 36 weeks after conception, your baby is developing a firm grasp.

Your baby’s toenails have reached the tips of his or her toes. His or her brain and nervous system are working better every day. This developmental process will continue through childhood and adolescence.

By now your baby may be close to 13 1/2 inches (340 millimeters) long from crown to rump and weigh nearly 6 1/2 pounds (2,900 grams).

Week 39: Placenta provides antibodies

Thirty-nine weeks into your pregnancy, or 37 weeks after conception, your baby’s chest is becoming more prominent. For boys, the testes continue to descend into the scrotum. For girls, the labia majora is well developed.

Your baby has enough fat under the skin to maintain body temperature as long as there’s a little help from you. The placenta continues to supply your baby with antibodies that will help fight infection the first six months after birth. If you breast-feed your baby, your milk will provide additional antibodies.

Week 40: Your due date arrives

Forty weeks into your pregnancy, or 38 weeks after conception, your baby may be more than 14 inches (360 millimeters) long from crown to rump and weigh about 7 1/2 pounds (3,400 grams). Remember, however, that healthy babies come in different sizes.

Don’t be alarmed if your due date comes and goes without incident. It’s just as normal to deliver a baby a week or two late — or early — than it is to deliver on your due date.

 
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Posted by on December 31, 2009 in Our Days

 

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