Twin pregnancy as a model for studies in fetal cortisol concentrations in labour: relation to prostaglandins, prolactin and ACTH.

Cortisol and prostaglandins were measured in umbilical cord blood obtained from 50 twin pregnancies at caesarean section performed either before or during labour. Umbilical artery cortisol concentrations did not differ between twin I and II before labour or in the latent stage. During active labour cortisol levels were significantly higher in twin I than in twin II. Maternal cortisol levels did not correlate with cord blood cortisol levels in either twin before active labour, nor did the rise in maternal cortisol correlate with the cortisol level in twin I; maternal cortisol levels did, however, correlate with cortisol levels in twin II during active labour. Prostaglandins E(PGE), F 2 alpha (PGF 2 alpha), 13,14-dihydro-15-keto F 2 alpha (PGFM) and ACTH were measured in cord vein blood. PGE values did not differ between twin I and II before active labour. During active labour PGE levels were significantly greater in twin I and correlated with raised cortisol levels. No differences were seen at any stage in PGE and PGFM levels between twins I and II although PGFM levels increased in both twins during active labour. ACTH and prolactin levels did not increase during labour and were similar in twins I and II. The rise in fetal cortisol during active labour is primarily of fetal origin and PGE may be involved in stimulating cortisol production in the fetus.