Your Baby’s Development: The Second Trimester

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When is the second trimester?

The second trimester is week 13 through week 26 of your pregnancy. During this time, your baby continues to grow, develop and change almost daily.

How big is my baby?

When the second trimester starts, your baby is about 3 inches long. Your doctor might tell you your baby measures a certain length “from crown to rump.” This means your baby is being measured from the top of its head to its bottom (instead of head to toe) because the legs are curled up to the baby’s stomach.

At the beginning of the second trimester, your baby’s head is the biggest part of his or her body. During the next few weeks, the rest of your baby’s body will get longer in order to catch up. By the end of the second trimester, your baby may be 9 inches long—or even longer.

When will I start to feel my baby move?

Your baby is moving almost all the time, but you probably won’t feel anything until about the 20th week of pregnancy. At first, you’ll just notice a fluttering feeling and may not even be sure if it’s your baby or not. Soon enough, the movements will become very noticeable. Other people might even be able to see your belly move when your baby “kicks.”

Your baby’s movements are helping him or her practice for life outside your body. Muscles grow stronger as your baby learns to kick, suck and open and close his or her hands. Your baby is also practicing making faces, such as frowning, smiling and squinting.

When will I know my baby’s sex?

An ultrasound may be able to reveal your baby’s sex a few weeks into the second trimester. If you have an ultrasound then, you may be able learn your baby’s sex, if you want to, but keep in mind your baby has to be in an ideal position for the doctor or technician to see the sex organs.

Other highlights of the second trimester

  • Your baby starts hearing certain sounds, such as your heartbeat, by about the 18th week of pregnancy. After the 18th week, the baby’s hearing improves and he or she will be able to hear your voice.
  • Your baby’s eyes may open as early as the 20th week. Before this, the eyelids have been sealed shut. However, your baby’s eyes can’t see anything until the third trimester.
  • Fingerprints and footprints are well established by the middle of the second trimester. They appear on the hands first, then the feet. Fingerprints improve the baby’s grip.
  • Fine hair and a white waxy substance cover and protect your baby’s skin. The skin is very thin, loose and wrinkled. In the third trimester, some fat will start to show up under the skin to fill it in a little.