Plasma progesterone in the umbilical vessels at vaginal delivery of term infants.

The influence of stress and related factors on umbilical-cord vessel progesterone concentrations have been investigated in 150 vaginal deliveries. Cord vein progesterone levels were greater in breech deliveries than in forceps deliveries and in vaginal deliveries by maternal effort alone. Within the forceps group there was no difference in cord vessel progesterone concentrations between lift-out, mid-cavity or rotational forceps deliveries. Levels of progesterone were significantly greater in forceps deliveries where the infant was clinically distressed (P less than 0.01). Similarly, within the normal group progesterone levels were greater in a stressed group of infants, where cord vein pH, artery pH, Apgar score at 1 min or birthweight fell below the 10th centile for the study group. No differences in plasma progesterone concentration were found with labour commencing spontaneously or by induction, nor did the sex of the infant appear to influence this hormone. Progesterone levels were higher in samples from primiparae than in those from multiparae due to a small number of primiparae who had excessively long labours and high progesterone concentrations. There was, however, no strong statistical correlation between length of labour and progesterone concentrations.