Direct ultrasonographic measurement of fetal lung length in normal pregnancies and pregnancies complicated by prolonged rupture of membranes.

Fetal lung length was measured directly with ultrasonography in 20 patients with prolonged rupture of membranes, commencing before 25 weeks' gestation. Measurements were made weekly and compared with data collected from 310 normal pregnancies. Measurement of fetal lung length by ultrasonography was a good predictor of pulmonary hypoplasia, predicting greater than 90% of cases. There was a good correlation between lung size assessed by the last ultrasonographic examination and lung weight postmortem (r = 0.783, p less than 0.05). Lung length measurements were superior to fetal chest circumference measurements in the identification of pulmonary hypoplasia. There was a significant negative association between the amount of amniotic fluid and pulmonary hypoplasia (p less than 0.05). There were fetuses with pulmonary hypoplasia that had respiratory movements seen at the majority of ultrasonographic examinations.