Fetal lung maturation in diabetic pregnancy

The increased incidence of the idiopathic respiratory distress syndrome (IRDS) in infants of diabetic mothers may be explained by preterm delivery and asphyxia but the metabolic derangement per se may also be responsible for the inadequate production of surfactant. Experimental studies of the underlying mechanisms in the lungs of fetuses of pregnant diabetic rats have shown a decreased formation of the two major surfactant phospholipids disaturated phosphatidyl choline and phosphatidyl glycerol. In addition, the activities of key enzymes responsible for the production of these phospholipids are decreased in the fetal lung tissue. Inadequate utilization of pulmonary glycogen for surfactant biosynthesis has also been observed. Furthermore, experimental studies support that other changes than fetal hyperinsulinaemia are needed to produce a state of disturbed surfactant production. In human diabetic pregnancy strict metabolic control allows the fetal lungs to mature in a near-normal fashion. The presence of phosphatidyl glycerol in the amniotic fluid seems to be the best available predictor of lung maturity in diabetic pregnancy, in which both the lecithin/sphingomyelin ratio and amniotic fluid cytology may result in false-positive and false-negative values. The trend towards extension of delivery to term will undoubtedly diminish the need for estimation of fetal lung maturity by amniocentesis. Avoiding preterm delivery and adhering to strict metabolic control of the maternal diabetes would be expected to decrease the neonatal respiratory problems in diabetic pregnancy.