Human Fetal and Maternal Plasma Oestrogens and the Onset of Labour

Summary Levels of unconjugated oestrone and oestradiol were measured in maternal peripheral and umbilical arterial and venous plasma. The levels before and after the spontaneous onset of labour were compared, samples being obtained either at elective Caesarean section or at normal delivery following labour of spontaneous onset. In the umbilical circulation, the mean concentrations of both oestrone and oestradiol were higher in the vein than in the artery, but the V‐A difference was highly significant only for oestrone (P<0.001). The main positive finding in relation to labour was that in the umbilical vein plasma, the oestrone level was significantly higher (P<0.01) after labour than before its onset, the mean value (±S.E.) in the patients having an elective Caesarean section being 10.9 (±1–4) ng./ml., compared with a level of 17.1 (±1.6) ng./ml. in the group delivering spontaneously. In the maternal peripheral circulation there was no appreciable change in the level of oestrone or oestradiol in relation to labour. It is concluded that the increase in umbilical vein oestrone may depend on a change in the placental metabolism of oestrogens related to labour, and probably reflects more complex endocrine changes concerned in the control of human parturition.