It's normal for babies to have quiet periods in utero, and a temporary dip in activity could just mean that your baby is sleeping or he's low on energy because you haven't eaten in a while. However, if you sense an overall slowdown in movement, call your doctor. A long lull could signal oligohydramnios, or low amniotic fluid.
If you're uncertain about how often your baby is moving, take time out to count fetal kicks. Babies respond when their mom eats, so after breakfast or dinner, sit in a quiet room and just focus on how many times the baby is moving. You should detect at least 10 movements in two hours. If you don't, call your healthcare provider.
Low amniotic fluid affects about 10 percent of pregnancies. Often, the mother is simply dehydrated, and drinking plenty of water will resolve the problem. However, oligohydramnios may also be caused by a rupture in the amniotic sac, the placenta's failure to work properly, or rarely, a defect involving the baby's kidneys or bladder (amniotic fluid is actually baby's urine). In such cases, bed rest can minimize fluid loss and prolong your pregnancy.
If you're experiencing this problem after the 38th week of pregnancy or if your baby shows signs of distress, your doctor may induce delivery to avoid the danger of the cord getting compressed, cutting off blood flow to the baby. Amniotic fluid serves as a cushion for the umbilical cord, preventing baby from crimping or crushing his own lifeline. --Marguerite Lamb