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Pregnancy and Fetal Development

Picture of First Trimester (12 Weeks)

Picture of First Trimester (12 Weeks)

A baby in the first trimester at 12 weeks has the following features:

  • Muscles and nerves are coordinated. Baby can make a fist.
  • The baby's eyelids are closed and will not open until 28 weeks' gestation.
  • The growth of the head is slower and the baby has grown longer. Your baby weighs nearly one ounce and is about 3 inches long.
  • The external sex organs show the baby's gender, but this is not distinguishable on ultrasound until the second trimester or later.
Image Source: 043705B000261-01 Copyright © LookatSciences / Phototake -- All rights reserved.

Text Reference: American Pregnancy Association: “Fetal Development: First Trimester”