The Inside Story: Your Baby in Week Twenty-Eight

Your little one weighs about 2-1/2 pounds now and is still growing!

Your baby can open and close his eyes at will now, and he'll suck his thumb if he's so inclined. He's probably close to 2-1/2 pounds. If your baby is a boy, his testes will soon descend into his scrotum.

Your baby's brain is developing rapidly right now. An ultrasound of your baby at 28 weeks shows a head that is large in proportion to his body; at birth a human baby's brain accounts for a whopping 12 percent of his body weight. Your baby already has the 100 billion or so brain cells he'll have at birth. However, he still has to build connections between them to form the neurological network that will give him control over everything from his footsteps to his speech.

During the first year of life, a baby's brain grows faster than the brain of any other mammal. This burns a lot of calories; your baby will require a diet that's 50 percent fat to fuel all that growth. Luckily, breast milk and formula are both designed to offer that balance. It's a good thing that this brain-building process takes place after birth; otherwise your baby's head would be too large to fit through your pelvis.

The placental blood flow is increasing dramatically to support your baby's rapid growth during the 3rd trimester, and the placenta itself is growing. For example, the placenta weighed only about 6 ounces during your 20th week of pregnancy, but by now it's probably close to 15 ounces.

Originally published in You & Your Baby: Pregnancy.

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