Abstract

Total DNA was estimated in the lungs of 80 fetuses and newborn infants varying in gestation from 14 weeks to term. In fetuses of appropriate weight for gestational age total lung DNA increased at a constant rate from about 35 mg at 17 weeks' gestation to 480 mg at term. The lungs of immature fetuses were heavier and contained more DNA relative to body weight than did those of mature infants. Small-for-dates infants had lower lung DNA levels for gestation than infants with weights appropriate for gestational age, but there was no difference when lung DNA was corrected for body weight. Lung hypoplasia defined in terms of lung/body weight ratio was associated with low lung DNA content for gestation, even when corrected for body weight. The total lung DNA at 34-40 weeks' gestation in infants with lung hypoplasia associated with fetal anuria or urinary outflow obstruction was equivalent to that seen in normal fetuses at 20-22 weeks' gestation. We conclude that the early second trimester is a critical period for human fetal lung growth.