An abnormally small amount of amniotic fluid surrounding the fetus in the uterus during pregnancy: Oligohydramnios can occur if the placenta is not functioning properly, if there is something wrong with the fetal urinary tract, or if a pregnancy goes beyond 41 weeks' gestation.

If oligohydramnios takes place later in pregnancy, the pressure of the uterus on the fetus may cause deformity; such as, clubfoot when a foot has been twisted to one side or when an ankle, a heel, or toes are twisted into a shape that is not normal.