Constrained by the limits of the uterus, the baby's movements are less grand during the final weeks of pregnancy.

The fetus spends the final four to six weeks of pregnancy gaining weight in preparation for his entry into the world. The weight gain gives the baby "the energy stores to insulate birth, so the child doesn't get cold, and to have enough energy in the fat to survive the first day or two after birth until hunger occurs and the connection between sucking and no longer being hungry is made.

"Typically babies will lose up to 10 percent of their weight in the first couple of days after their birth. At that point they figure out that the pain in their bellies will go away if they suck," explains Dr. Joshua Copel, professor of obstetrics and gynecology and pediatrics at Yale University School of Medicine.

In the weeks just before delivery, the fetus often seems quieter. "It's almost as if there isn't enough space for the baby to wind up and take a real good whack at mom's bladder. Movements are still there, but they're not as large as when there's more amniotic fluid relative to the size of the baby earlier," says Dr. Copel.