What are congenital sequences?

Cascade of anomalies triggered by one irritating aberration, one aberration leads to secondary effects in other organs. Oligohydramnios (Potter) sequence (caused by chronic leakage of amniotic fluid cause of rupture, or uteroplacental insufficiency from maternal HTN/toxemia, or renal agenesis in fetus so no urine constitutes amnion. We get fetal compression flattened facies and positional abnormalities of hands and feet, dislocated hips, hypoplastic lungs, nodules in amnion.