Relation between the amniotic fluid lecithin/sphingomyelin ratio, fetal cord blood corticosteroid levels and the duration of induced labour.

In serial samples of amniotic fluid from 24 patients in induced labour, the rate of change in the lecithin/sphingomyelin (L/S) ratio correlated significantly with the duration of labour. Cord serum 11-hydroxycorticosteroid levels were lowest in the group of patients in which the L/S rose during labour, and highest in the group in which the L/S ratio fell. Cord serum 11-hydroxycorticosteroid levels correlated positively with the duration of labour. It would seem unlikely that the changes in L/S ratio occurring during labour are mediated by endogenous corticosteroids.