Increased acinar complexity with polyhydramnios.

We report 4 cases that presented a contradiction in terms of intrauterine lung growth. In all cases there was increased acinar complexity despite an array of influences known to be associated with pulmonary hypoplasia. In 2 of the 4 cases the lungs were severely hypoplastic by weight. Following an analysis of the factors operative in each case regarding lung growth, we conclude that diffuse increased acinar complexity occurs in selected cases with massive polyhydramnios. The observation is of importance because it is consonant with an intimate and dynamic relationship between amniotic fluid volume, lung fluid production, and fetal breathing movements in normal intrauterine lung growth and maturation. Although lung hypoplasia is known to occur in association with polyhydramnios, the reported alterations in lung structure were not previously observed.