Effect of labour on the lecithin/sphingomyelin ratio in serial samples of amniotic fluid

Serial samples of amniotic fluid were taken from 48 patients during labour. The lecithin/sphingomyelin (L/S) ratio was estimated and found to rise in 52 per cent, remain almost unchanged in 33 per cent and fall in 15 per cent. The rate of rise in the L/S ratio seemed inversely related to the length of labour.