The lecithin/sphingomyelin ratio in cases associated with fetomaternal disease

The efficacy of correlating the L/S ratio in the amniotic fluid with fetal lung maturity has been substantiated in normal pregnancies. In gestations complicated by fetomaternal diseases, however, the assay is less reliable. This study involves 555 pregnancies in which there was a significant maternal, fetal, or placental disorder. The L/S ratio was related to fetal respiratory maturity as measured by Dubowitz criteria and the occurrence of RDS. The results show that pre-eclampsia, chronic hypertension, diabetes (Class D, E, F), significant cardiovascular disease, severe hemoglobinopathies, various congenital anomalies, chronic placental insufficiency, and prolonged ruptured membranes accelerated the L/S ratio. Conversely, mild diabetes (Class B, C), intrinsic renal disease, hepatitis, collagen disease, hydrops fetalis, syphilis, and toxoplasmosis were associated with a delay in the L/S ratio. A significant increase in erroneous responses was noted in these patients when the L/S ratio was correlated to infant maturity and to the incidence of RDS. Possible mechanisms for these findings are discussed.