Weeks 13-16

The baby can make sucking motions with his mouth now.   The baby's nervous system allows him to feel pain.  (New England Journal of Medicine)

The baby can make active movements including kicking and even somersaults.

Muscle tissue and bone continue to form, creating a more complete skeleton. The baby's sex becomes apparent during this time.

The scalp hair pattern has formed.

More developed facial muscles may lead to various facial expressions such as squinting or frowning.

Weeks 17-18

Fat stores begin to develop under the baby's skin. The fat will provide energy and help keep the baby warm after birth.

The baby's ears begin to stand out on the sides of his or her head. As the nerve endings from the baby's brain "hook up" to the ears, the baby may hear the mother's heart beating, her stomach rumbling or blood moving through the umbilical cord. He or she may even be startled by loud noises.

Week 20

The 20th week is halfway into the pregnancy. ( 18 weeks after conception) The baby's delicate skin is protected with a greasy, cheese-like coating called vernix caseosa.

Fingernails and toenails appear.

The mother may be able to feel your baby's movements at this point.  This is known as quickening.

The baby's sex organs are visible on ultrasound.

By now the baby may be about 6 1/3 inches (160 millimeters) long from crown to rump and weigh more than 11 ounces (320 grams).

Weeks 21- 24

The baby is becoming more active and can swallow. He begins to have rapid eye movements. The tongue will soon develop taste buds. Fingerprints and footprints are forming.

For boys, the testes are beginning to descend from the abdomen. For girls, the uterus and ovaries are in place - complete with a lifetime supply of eggs.

The baby is regularly sleeping and waking. Real hair is beginning to grow on his or her head.

With intensive medical care, some babies born this week may be able to survive.

Weeks 25-27

The baby's hands are fully developed. Exploring the structures inside the mother's uterus may become baby's prime entertainment.

This week marks the end of the second trimester. At 27 weeks, or 25 weeks after conception, the baby's lungs, liver and immune system are continuing to mature - and he or she has been growing like a weed.

The baby's crown-to-rump length may have tripled since the 12-week mark.

Continue to 3rd Trimester