Second Trimester of Pregnancy

 

Week 13: Urine forms

Thirteen weeks into your pregnancy, or 11 weeks after conception, your baby's intestines have moved from the umbilical cord to your baby's abdomen. Your baby is also beginning to form urine and discharge it into the amniotic fluid.

Tissue that will become bone is also developing around your baby's head and within his or her arms and legs. Tiny ribs may soon appear.

Week 14: Baby's sex becomes apparent

Fourteen weeks into your pregnancy, or 12 weeks after conception, your baby's arms have almost reached the length they'll be at birth and your baby's neck has become more defined. Red blood cells are forming in your baby's spleen.

Your baby's sex will become apparent this week or in the coming weeks.

By now your baby may be almost 3 1/2 inches (87 millimeters) long from crown to rump and weigh about 1 1/2 ounces (45 grams).

Week 15: Baby's skeleton develops bones

Fifteen weeks into your pregnancy, or 13 weeks after conception, your baby is growing rapidly. Your baby's skeleton is developing bones, which will become visible on ultrasound images in a few weeks. Your baby's scalp hair pattern also is forming.

Week 16: Facial expressions are possible

Sixteen weeks into your pregnancy, or 14 weeks after conception, your baby's eyes have begun to face forward and slowly move. The ears are close to reaching their final position. More-developed facial muscles may lead to various expressions, such as squinting and frowning. Your baby also can now make sucking motions with his or her mouth.

Although still too slight to be felt, your baby's movements are becoming coordinated and can be seen during ultrasound exams.

By now your baby may be more than 4 1/2 inches (120 millimeters) long from crown to rump and weigh nearly 4 ounces (110 grams).

Week 17: Fat accumulates

Seventeen weeks into your pregnancy, or 15 weeks after conception, fat stores begin to develop under your baby's skin. The fat will provide energy and help keep your baby warm after birth.

Week 18: Baby begins to hear

Eighteen weeks into your pregnancy, or 16 weeks after conception, your baby's ears begin to stand out on the sides of his or her head. As the nerve endings from your baby's brain "hook up" to the ears, your baby may hear your heart beating, your stomach rumbling or blood moving through the umbilical cord. He or she may even be startled by loud noises.

By now your baby may be 5 1/2 inches (140 millimeters) long from crown to rump and weigh 7 ounces (200 grams).

Week 19: Baby's uterus forms

Nineteen weeks into your pregnancy, or 17 weeks after conception, your baby's hearing continues to improve. He or she may pick up your voice in conversations — although it's probably hard to hear clearly through the amniotic fluid and protective paste covering your baby's ears.

For girls, the uterus and vagina may be forming this week.

Week 20: The halfway point

Halfway into your pregnancy, or 18 weeks after conception, your baby's delicate skin is protected with a greasy, cheese-like coating called vernix caseosa.

You may be able to feel your baby's first movements, also known as quickening.

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

Week 21: Baby can swallow

Twenty-one weeks into your pregnancy, or 19 weeks after conception, your baby is about to gain more weight. By this week your baby is becoming more active and can swallow.

Week 22: Baby's hair becomes visible

Twenty-two weeks into your pregnancy, or 20 weeks after conception, your baby is completely covered with a fine, down-like hair called lanugo. The lanugo helps hold the vernix caseosa on the skin. Your baby's eyebrows may be visible.

By now your baby may be 7 1/2 inches (190 millimeters) long from crown to rump and weigh 1 pound (460 grams).

Week 23: Fingerprints and footprints form

Twenty-three weeks into your pregnancy, or 21 weeks after conception, your baby's skin is wrinkled, more translucent than before and pink to red in color.

This week your baby begins to have rapid eye movements. Your baby's 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.

Week 24: Real hair grows

Twenty-four weeks into your pregnancy, or 22 weeks after conception, your baby is regularly sleeping and waking. Real hair is beginning to grow on his or her head.

By now your baby may be slightly longer than 8 inches (210 millimeters) from crown to rump and weigh more than 1 1/3 pounds (630 grams).

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

Week 25: Exploration continues

Twenty-five weeks into your pregnancy, or 23 weeks after conception, your baby's hands are fully developed — although the nerve connections to the hands have a long way to go. Exploring the structures inside your uterus may become baby's prime entertainment.

Week 26: Baby's fingernails develop

Twenty-six weeks into your pregnancy, or 24 weeks after conception, your baby has fingernails.

Your baby's lungs are beginning to produce surfactant, the substance that allows the air sacs in the lungs to inflate — and keeps them from collapsing and sticking together when they deflate.

By now your baby may be 9 inches (230 millimeters) long from crown to rump and weigh nearly 2 pounds (820 grams).

Week 27: Second trimester ends

This week marks the end of the second trimester. At 27 weeks, or 25 weeks after conception, your baby's lungs, liver and immune system are continuing to mature — and he or she has been growing like a weed. Your baby's crown-to-rump length may have tripled since the 12-week mark.