18 Weeks!

How your baby's growing: Head to bottom, your baby is approximately 5 1/2 inches long (about the length of a large sweet potato) and she weighs almost 7 ounces. She's busy flexing her arms and legs — movements that you'll likely start noticing more and more. Her blood vessels are visible through her thin skin and her ears are now in position and stand out from her head. Myelin (a protective covering) is beginning to form around her nerves, a process that will continue for a year after she's born. If you're having a girl, her uterus and Fallopian tubes are formed and in place. If your baby is a boy, his genitals are noticeable, though he may hide them from you during an ultrasound.

17 weeks

How your baby's growing: Your baby weighs about 5 ounces now, and he's around 5 inches long — about the size of a large onion. He can move his joints, and his skeleton — until now rubbery cartilage — is starting to harden to bone. His sense of hearing is also developing. The umbilical cord, his lifeline to the placenta, is growing stronger and thicker.

16 weeks

How your baby's growing: At 4 1/2 inches long (head to bottom) and 3 1/2 ounces, your baby is about the size of an avocado. In the next three weeks, she'll go through a tremendous growth spurt, though, doubling her weight and adding inches to her length. Her lower limbs are much more developed now. Her head is more erect than it has been, and her eyes have moved toward the front of her head. Your baby's ears are close to their final position, too. Some of her more advanced body systems are working, including her circulatory system and urinary tract. Her heart is now pumping about 25 quarts of blood each day, circulating her total blood volume through her body many times. (By the end of your pregnancy, this will increase to about 190 quarts.) The patterning of her scalp has begun, though her hair isn't recognizable yet. Although closed, her eyes are moving (slowly), and she's even started growing toenails.