Fetal abnormality is one of several possible causes of polyhydramnios. Your doctor may call for amniocentesis if they suspect that a problem with the fetus is causing the condition. Several types of fetal health complications can cause polyhydramnios. Problems with swallowing, the gastrointestinal tract, and with the central nervous system all prevent the fetus from ingesting amniotic fluid, thereby contributing to its buildup in the uterus. If the cause of polyhydramnios lies with the fetus, this can be a sign of a condition that doctors will monitor during and after the pregnancy.