Changes in human amniotic fluid lecithin/sphingomyelin ratio and dipalmitoyl lecithin associated with maternal betamethasone therapy.

In an effort to understand the biochemical changes responsible for the decreased incidence of neonatal RDS observed in premature infants delivered after maternal glucocorticoid therapy we have compared quantitative changes in L/S ratio and qualitative changes in dipalmitoyl lecithin in serial amniotic fluid samples from 20 pregnant women treated with betamethasone and 11 patients who had repeated amniocentesis at similar gestational age but did not receive glucocorticoids. Initial L/S ratio values were not significantly different between treated (1.24 +/- 0.24 [S.D.]) and control (1.09 +/- 0.29 [S.D.]) groups but the values obtained within 1 week after therapy (1.49 +/- 0.21 [S.D.]) were significantly higher (t=3.8; p less than 0.01) than those obtained after a similar period in the untreated group (1.24+/- 0.29 [S.D.]). However, only one of the treated patients reached a mature L/S ratio (2.0 or more). Simultaneously, 10 of 17 treated patients exhibited increases in the amount of dipalmitoyl lecithin within the first week after treatment, wheras no change was detected in serial samples from six control patients (p = 0.016). These results indicate that qualitative changes in amniotic fluid lecithin composition are a part of the fetal response to glucocorticoids which may be responsible for the decreased incidence of RDS observed after treatment.