How your baby's growing:Head to rump, your baby is about 5 1/2 inches long (about the length of a bell pepper) and he weighs almost 7 ounces. He's busy flexing his arms and legs — movements that you'll start noticing more and more in the weeks ahead. His blood vessels are visible through his thin skin, and his ears are now in their final position, although they're still standing out from his head a bit. A protective covering of myelin is beginning to form around his nerves, a process that will continue for a year after he's born. If you're having a girl, her uterus and fallopian tubes are formed and in place. If you're having a boy, his genitals are noticeable now, but he may hide them from you during an ultrasound.

See what your baby looks like this week.

How your baby's growing:Your baby's skeleton is changing from soft cartilage to bone, and the umbilical cord — his lifeline to the placenta — is growing stronger and thicker. Your baby weighs 5 ounces now (about as much as a turnip), and he's around 5 inches long from head to bottom. He can move his joints, and his sweat glands are starting to develop.

See what your baby looks like this week.

How your baby's growing:Get ready for a growth spurt. In the next few weeks, your baby will double his weight and add inches to his length. Right now, he's about the size of an avocado: 4 1/2 inches long (head to rump) and 3 1/2 ounces. His legs are much more developed, his head is more erect than it has been, and his eyes have moved closer to the front of his head. His ears are close to their final position, too. The patterning of his scalp has begun, though his locks aren't recognizable yet. He's even started growing toenails. And there's a lot happening inside as well. For example, his heart is now pumping about 25 quarts of blood each day, and this amount will continue to increase as your baby continues to develop.

See what your baby looks like this week. (Or see what fraternal twins look like in the womb this week.)

How your baby's growing:Your growing baby now measures about 4 inches long, crown to rump, and weighs in at about 2 1/2 ounces (about the size of an apple). He's busy moving amniotic fluid through his nose and upper respiratory tract, which helps the primitive air sacs in his lungs begin to develop. His legs are growing longer than his arms now, and he can move all of his joints and limbs. Although his eyelids are still fused shut, he can sense light. If you shine a flashlight at your tummy, for instance, he's likely to move away from the beam. There's not much for your baby to taste at this point, but he is forming taste buds. Finally, if you have an ultrasound this week, you may be able to find out whether your baby's a boy or a girl! (Don't be too disappointed if it remains a mystery, though. Nailing down your baby's sex depends on the clarity of the picture and on your baby's position. He may be modestly curled up or turned in such a way as to "hide the goods.")

See what your baby looks like this week.

How your baby's growing:This week's big developments: Your baby can now squint, frown, grimace, pee, and possibly suck his thumb! Thanks to brain impulses, his facial muscles are getting a workout as his tiny features form one expression after another. His kidneys are producing urine, which he releases into the amniotic fluid around him — a process he'll keep up until birth. He can grasp, too, and if you're having an ultrasound now, you may even catch him sucking his thumb.

In other news: Your baby's stretching out. From head to bottom, he measures 3 1/2 inches — about the size of a lemon — and he weighs 1 1/2 ounces. His body's growing faster than his head, which now sits upon a more distinct neck. By the end of this week, his arms will have grown to a length that's in proportion to the rest of his body. (His legs still have some lengthening to do.) He's starting to develop an ultra-fine, downy covering of hair, called lanugo, all over his body. Your baby's liver starts making bile this week — a sign that it's doing its job right — and his spleen starts helping in the production of red blood cells. Though you can't feel his tiny punches and kicks yet, your little pugilist's hands and feet (which now measure about 1/2 inch long) are more flexible and active.