Second trimester: What's happening to your baby

Week 14

Hair and eyebrows are growing.
Heartbeat is strong enough to hear with ultrasound.
Starts to drink amniotic fluid (the fluid surrounding the baby).

Week 15

Middle ear bones harden, so baby can hear.

Week 16

Fine, downy hair called "lanugo" appears all over body and face.
External genital organs are developed enough to be seen with ultrasound.
Developing skin is transparent.

Week 17

Baby can hear sounds outside the mother's body and will jump when startled.
Fingernails and toenails begin to appear.
Baby may begin thumb-sucking.

Week 18

Baby is moving much of the time now.
Skeleton would be clearly outlined if X-ray was performed.
Baby measures 8 inches long.

Week 19

Buds for permanent teeth begin to form.
Baby drinks amniotic fluid, which is filtered through the kidneys and excreted back into the amniotic sac.
Baby may get hiccups.

Week 20

Baby's movements can now be felt by mother.
Baby is 8 1/2 inches long and weighs 8 to 16 oz.

Week 21

Skin is becoming opaque.
Tongue is fully developed.

Week 22

Vernix, a greasy, white, cheesy-looking substance, is beginning to form on the baby's skin to protect it (most of the vernix will disappear before birth).

Week 23

Heartbeat can be heard with a stethoscope.

Week 24

Vital organs are developed enough for the baby to survive outside the womb.
Lungs are immature, however, and the baby would need breathing assistance if born now.
Baby measures about 14 inches long and weighs 1 to 1 1/2 pounds.

Week 25

Bone centers begin to harden.

Week 26

Fat stores are beginning to form.