Week 5By this point in your pregnancy a distinct shape begins to form. The neural tube, which will eventually form into the spinal cord and brain, runs from the top to the bottom of the embryo. A bulge in the center of the embryo will develop into your baby's heart. At this time, the placenta develops.
Week 8Fingers and toes are just beginning to form this week, and the arms can even flex at the elbows and wrists. The eyes are becoming more obvious because they’ve begun to develop pigment (color) in the retina (back of the eye).
Also, the intestines are getting longer and there isn’t enough room for them in the baby’s abdomen, so they protrude into the umbilical cord until week 12.
Week 11From this week until week 20, your baby will be growing rapidly — increasing in size from about 2 inches (5 cm) to about 8 inches (20 cm) from crown to rump. To accommodate all this growth, the blood vessels in the placenta are increasing in both size and number to provide the baby with more nutrients.
Facial development continues as the ears move toward their final position on the sides of the head.
Week 14By this week, some fine hairs have developed on your baby's face. This soft colorless hair is called lanugo. It will eventually cover most of your baby's body until it is shed just before delivery.
By now, your baby's genitals have fully developed, though they may still be difficult to detect on an ultrasound examination. In addition, your baby starts to produce thyroid hormones because the thyroid gland has matured.
Week 18Ears move to their final position and they stand out from the head. In the coming weeks, your baby will probably be able to hear! Your baby's eyes are also developing — they're now facing forward rather than to the sides.
Until now, your baby's bones had been developing but were still soft. This week, they begin to harden, or ossify. Some of the first bones.
Week 22The amniotic fluid that has cushioned and supported your baby in the uterus now serves another purpose. The intestines have developed enough that small amounts of sugars can be absorbed from the fluid that is swallowed and passed through the digestive system to the large bowel. Almost all of your baby's nourishment, however, still comes from you through the placenta.
Week 28At your next prenatal appointment, your health care provider may tell you whether your baby is headfirst or feet- or bottom-first (called breech position) in the womb. Babies who are in the breech position may need to be delivered by cesarean section. Your baby still has 2 months to change position. Most will change position on their own.
Week 32The final touches are being placed on your baby masterpiece. Eyelashes, eyebrows, and the hair on your baby's head are evident. The lanugo hair that has covered your baby since the beginning of the second trimester is falling off, although some may remain on the shoulders and back at birth.
Week 35Your baby already weighs about 5 pounds, 5 ounces (2,400 grams), but this week begins your baby's most rapid period of weight gain — about 8 to 12 ounces (226 to 340 grams) each week! Fat is being deposited all over your baby's body, especially around the shoulders.
Week 40Newborns often have heads temporarily misshapen from the birth canal and may be covered with vernix and blood. Your baby's skin may have skin discolorations, dry patches, and rashes — these many variations are completely normal. Only 5% of women deliver on their estimated due dates, and many first-time mothers find themselves waiting up to 2 weeks after their due date for their baby to arrive.