Your Baby's Development
From this week until week 20, your baby will be growing rapidly - increasing in size from about 1.7 to 2.4 inches (44 to 60 millimeters) and 0.3 ounces (8 grams) to about 5.5 to 6.3 inches (14 to 16 centimeters) and 9 ounces (260 grams) by week 20. To accommodate all this growth, the blood vessels in the placenta are increasing both in size and in 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. If you saw a picture of your baby now, you'd think you had a genius on your hands - the baby's head accounts for about half of the body length!

Your baby's reproductive organs develop rapidly this week. First, a tiny bit of tissue forms your baby's external genitals, even though you can't yet tell whether you'll have a boy or girl. Next, the tissue develops into either a penis or a clitoris and labia majora. By the end of this week, your baby's external genitalia are recognizable.

Your Body
Nourishing your baby usually requires that you gain weight - and in most cases, the recommended weight gain is 25 to 35 pounds over the course of the pregnancy. To accommodate the baby's weight, the placenta, the amniotic fluid, increased blood volume, and an enlarged uterus and breasts, a woman usually gains 2 to 5 pounds during the first trimester, 13 pounds during the second trimester, and 11 pounds during the last trimester. If you were overweight or underweight before pregnancy, your health care provider may have different recommendations for weight gain.