6 weeksThe nose, mouth, and ears that you'll spend so much time kissing in eight months are beginning to take shape. His pituitary gland is forming, as are the rest of his brain, muscles, and bones. Right now, your baby is a quarter of an inch long, about the size of a lentil.
9 weeksAbout the size of a grape — and weighs just a fraction of an ounce. Morning sickness and other physical symptoms out in full force for most women. The embryonic "tail" is completely gone.
12 weeksThe most dramatic development this week: reflexes.
Your baby's fingers will soon begin to open and close, his toes will curl, his eye muscles will clench, and his mouth will make sucking movements. Meanwhile, nerve cells are multiplying rapidly, and in your baby's brain, synapses are forming furiously. His intestines, which have grown so fast that they protrude into the umbilical cord.
16 weeksThe patterning of his scalp has begun, though his locks aren't recognizable yet. 4 1/2 inches long (head to rump) and 3 1/2 ounces. Right now, he's about the size of an avocado.
19 weeksAbout the size of a large heirloom tomato. A waxy protective coating called the vernix caseosa is forming on her skin to prevent it from pickling in the amniotic fluid. Some research suggests that she may be able to hear your voice now.
24 weeksHe cuts a pretty lean figure at this point, but his body is filling out proportionally and he'll soon start to plump up. His lungs are developing "branches" of the respiratory "tree" as well as cells that produce surfactant, a substance that will help his air sacs inflate once he hits the outside world. His skin is still thin and translucent, but that will start to change soon.
26 weeksHe's inhaling and exhaling small amounts of amniotic fluid, which is essential for the development of his lungs. And he's continuing to put on baby fat. He now weighs about a pound and two-thirds and measures 14 inches (an English hothouse cucumber) from head to heel. The network of nerves in your baby's ears is better developed and more sensitive than before.
30 weeksShe weighs almost 3 pounds (like a head of cabbage). Her eyesight continues to develop, though it's not very keen; even after she's born, she'll keep her eyes closed for a ghttp://www.babycenter.com/6_your-pregnancy-30-weeks_1119.bc?intcmp=timeline
36 weeksShe now weighs almost 6 pounds (like a crenshaw melon) At the end of this week, your baby will be considered full-term. She's shedding most of the downy covering of hair that covered her body as well as the vernix caseosa, the waxy substance that covered and protected her skin during her nine-month amniotic bath.
40 weeksIt's hard to say for sure how big your baby will be, but the average newborn weighs about 7 1/2 pounds (a small pumpkin) and is about 20 inches long. His skull bones are not yet fused, which allows them to overlap a bit if it's a snug fit through the birth canal during labor. This so-called "molding" is the reason your baby's noggin may look a little conehead-ish after birth. Rest assured — it's normal and temporary.