First Trimester: The Baby at 12 Weeks
- The nerves and muscles begin to work together. Your baby can make a fist.
- The external sex organs show if your baby is a boy or girl. A woman who has an ultrasound in the second trimester or later might be able to find out the baby’s sex.
- Eyelids close to protect the developing eyes. They will not open again until the 28th week.
- Head growth has slowed, and your baby is much longer. Now, at about 3 inches long, your baby weighs almost an ounce.