Surfactant proteins in the diagnosis of fetal lung maturity. II. The 35 kd protein and phospholipids in complicated pregnancy.

The major surfactant protein with a molecular weight of 35 kd and also saturated phosphatidylcholine and phosphatidylglycerol were analyzed in specimens of amniotic fluid; 68 were from cases of maternal diabetes, 41 from preeclampsia or maternal hypertension, 26 from premature rupture of the fetal membranes, and 45 from normal pregnancies. The relationship between the individual surfactant components was studied after covariance adjustment for the length of gestation. In severe early-onset preeclampsia, the 35 kd surfactant protein/saturated phosphatidylcholine ratio was significantly higher than in the other pregnancies. In diabetic pregnancies (classes B to D without preeclampsia), the phosphatidylglycerol/saturated phosphatidylcholine ratio was lower than in the other pregnancies. Isolated surfactant complex showed similar abnormalities. In severe early-onset preeclampsia and insulin-dependent diabetes without vascular disease, the phosphatidylglycerol/saturated phosphatidylcholine ratio correlated negatively with fetal growth. In four samples of amniotic fluids from cases of severe early-onset preeclampsia, the 35 kd protein falsely predicted lung maturity. All had abnormally high 35 kd protein/saturated phosphatidylcholine ratios (greater than 2 SD of controls). According to the present results, the 35 kd protein may give a false mature test result in severe preeclampsia.