The urine production in the fetal kidneys is substantial for keeping the optimal volume of the amniotic fluid.

Oligohydramnion (reduced volume of amniotic fluid) or anhydramion (nearly absent amniotic fluid) is a common consequence of congenital malformations of kidneys and urinary tract. It may be caused either by insufficient urine production or by urinary tract obstruction.

In case of oligo/anhydramnion the following sequence develops (called as Potter sequence):

External compression of the fetus against uterus walls constrains its mobility, the lower extremities are deformed(club feet), the face has characteristic deformities caused by the pressure (beaked nose, low-set ears, recessive chin). The respiratory movements which are since the end of the second trimester necessary for the growth and maturing of the pulmonary tissue are also restricted. The lungs have normal appearance but are markedly reduced in size — pulmonary hypoplasia (ratio of lung weight to body weight is lower). The surface for the exchange of blood gases is too small and the newborn dies shortly after the birth of severe respiratory insufficiency.

Congenital renal malformations are nowadays exactly and early diagnosed by sonographic screening, often as early as 16 week of gestation. The most frequent anomalies in our autopsy group are lower urinary tract obstructions, multicystic renal dysplasia and bilateral renal agenesis. Simultaneous occurence of congenital malformations of reproductive and urinary system is common.