Picture of First Trimester (12 Weeks)

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.

Reviewed by William C. Shiel Jr., MD, FACP, FACR on August 21, 2009

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Text: Womenshealth.gov - Healthy Pregnancy: Stages of Pregnancy