Palmitic/stearic ratio of amniotic fluid in diabetic and nondiabetic pregnancies and its relationship to development of respiratory distress syndrome

Abstract

Amniotic fluid (AF) samples obtained from 64 patients within 72 hours of delivery of their infants were analyzed by gas-liquid chromatography to quantitate the individual fatty acids present in the hydrolysate of the lecithin fraction. The results were expressed as the palmitic/stearic (P/S) ratio, which we have considered to be a reflection of the relative amount of dipalmityl lecithin being secreted into the AF from the fetal lungs. Of the 64 patients studied, 31 were insulin-dependent diabetic patients and 33 were nondiabetic. Of the 31 infants of the diabetic mothers, eight developed the respiratory distress syndrome (RDS). Of the 33 infants of the nondiabetic mothers, seven developed RDS. In both the diabetic group and the nondiabetic group, each considered separately, the mean P/S ratio distinguished RDS from non-RDS patients (p < 0.001). In the diabetic patients RDS was not observed in association with a P/S ratio above 10.0. However, seven out of 23 infants who had P/S ratios below 10.0 failed to develop RDS. In the nondiabetic patients, RDS was not observed in association with a P/S ratio above 6.0. However, six out of 26 infants who had P/S ratios below 6.0 failed to develop RDS. Therefore, while there is a high correlation between the amount of AF lecithin palmitic acid and the development of RDS, the correlation is not absolute. The relationship between the P/S ratio and the development of RDS was different in diabetic as compared to nondiabetic subjects. The mean values of the P/S ratios in the diabetic and nondiabetic groups without RDS were not significantly different (p < 0.07). However, the infants of diabetic mothers developed RDS in association with P/S ratios that were, on the average, higher than those of infants who developed RDS and whose mothers were nondiabetic (p < 0.03). It is concluded that: (1) while the amount of AF dipalmityl lecithin is a good predictor of RDS, the relationship between the two is not absolute, (2) factors other than the ability of the fetal lung to secrete dipalmityl lecithin probably have an important influence on the development of RDS, and (3) the increased disposition of infants of diabetic mothers to develop RDS probably involves factors other than the ability of the fetal lung to secrete dipalmityl lecithin.