what causes oligohydramnios
Pathophysiology. Rupture of the membranes is the most common cause of oligohydramnios. However, because the amniotic fluid is primarily fetal urine in the latter half of the pregnancy, the absence of fetal urine production or a blockage in the fetus' urinary tract can also result in oligohydramnios.
It is not always possible to determine what causes low levels of amniotic fluid. Oligohydramnios can be caused by a continuous leaking of amniotic fluid. It can also occur when the fetus has kidney failure. After about four months of pregnancy, the kidneys of a normal fetus will produce the amniotic fluid. If the fetus has kidney abnormalities, the amount of amniotic fluid may be too low.