Week 13: Your pregnancy

Your baby's growth: Ribs and vocal cords

The fetus, which is now about 3 inches long and a little more than an ounce in weight, would fit into your cupped hands.

It's still fairly early in your pregnancy, but your baby is already capable of quite a lot. If you poke your stomach gently with your finger, she may begin to turn her head toward you. Some experts think this may be the beginning of the rooting reflex (looking for a nipple).

By now she can put a thumb into her mouth, although her sucking muscles aren't completely developed yet. And female infants have already accumulated about 2 million eggs in their ovaries, although this number will naturally drop to 1 million at birth.

Your baby's head growth has slowed down; this week her head makes up about half her body length. By week 21 her head will be about a third the size of her body, and by birth it will only be about a fourth.

Here's what else you can expect this week:

• Tiny ribs will develop.
• Vocal cords will begin to form.
• Eyelids will fuse together to protect her delicate eyes.
• Tissues and organs will continue to mature.
• Bone marrow, liver and spleen will be able to produce blood cells now.
• Fingerprints begin to form.

What's happening with you

• Increased comfort. Welcome to the second trimester, when most women begin to feel much more comfortable than they did in their earlier stages of pregnancy. The side effects of early pregnancy (frequent urination, fatigue, nausea, dizziness) lessen during the second trimester. Your uterus is still small enough so that you can easily go about your daily activities.
• Abdominal achiness. At 13 weeks the uterus starts growing upward into the abdomen, and you may feel some abdominal aches as the ligaments supporting the uterus stretch.
• Weight gain. Up until now you may not have gained much weight, but as your baby starts growing rapidly, you'll see your weight increase.
• Colostrum production. Even though birth is still months away, your breasts may already have started to make colostrum, the nutrient-rich fluid that will feed your baby for the first few days after birth.
• Breast changes. As the breasts enlarge, you may notice veins appearing under the skin and the areola enlarging and turning brown. Experts think this darker color around the nipple may be a visual cue for the breastfeeding baby.
• Stretch marks. You may also start to see the first signs of stretch marks on your abdomen, breasts, hips or buttocks. Since stretch marks are partly genetic, you may be able to predict ahead of time whether you'll experience them or not.

By applying moisturizing creams you can make your skin more elastic and can help reduce the itchiness that accompanies the development of stretch marks. Creams may also help reduce the severity of the marks, although it's difficult to prevent them from occurring entirely. The good news is that the marks will be less noticeable after pregnancy, when they'll probably fade to a more normal skin color.