D Renal obstruction or renal agenesis may cause oligohydramnios
Renal obstruction or agenesis causes oligohydramnios due to the fact that the fetus cannot excrete urine. During fetal life the fetus swallows the amniotic fluid and excretes through the kidneys and bladder. This is not necessary since the placenta removes waste from the fetus. Some urinary function can be observed during a sonographic examination. The bladder will fill and empty, ureters will be small and no hydronephrosis will be seen.