NBRC Registered Respiratory Therapist – Neonatal/Pediatric Specialty (RRT-NPS) Practice Test 2026 - Free RRT-NPS Practice Questions and Study Guide

Fetal urine becomes the main source of amniotic fluid after the first trimester, so when the kidneys fail to develop (renal agenesis), there is very little or no urine produced and amniotic fluid becomes severely reduced—oligohydramnios. This low fluid environment allows the fetus to be compressed, which leads to Potter sequence: distinctive facial features (Potter facies), limb deformities due to restricted movement, and lung hypoplasia from insufficient space and development. Polyhydramnios, by contrast, would indicate excess fluid often related to problems with swallowing or GI obstruction, not renal agenesis. So renal agenesis directly reduces amniotic fluid and drives the associated anomalies.