Development of the mature kidney begins between weeks 5 and 7 of gestation. Fetal urine production begins in early gestation and comprises the majority of the amniotic fluid in the second and third trimesters of pregnancy. The fetus continuously swallows amniotic fluid, which is reabsorbed by the gastrointestinal tract and then reintroduced into the amniotic cavity by the kidneys via urination. Oligohydramnios occurs if the volume of amniotic fluid is less than normal for the corresponding period of gestation. The fetal urine is critical to the proper development of the lungs by aiding in the expansion of the airways - alveoli, by means of hydrodynamic pressure and by also supplying proline which is a critical amino acid for lung development. Alveoli are the small sacs in the lungs that exchange oxygen with the blood. If the alveoli, and thereby the lungs, are underdeveloped at the time of birth the infant will not be able to breathe air properly and will go into respiratory distress shortly after birth due to pulmonary hypoplasia (underdeveloped lungs). This is the primary cause of death to<unk>  infants secondary to renal failure. The fetal urine also serves to cushion the fetus from being compressed by the mother's uterus as it grows.
Potter sequence
Lethal congenital contracture syndrome
Stafne defect
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Jordans' anomaly
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Renal dysplasia-limb defects syndrome
Crisscross heart