Inhibitory effects of hCG on uterine smooth muscle contractility and relationship between serum hCG concentration and onset of labour in the human

In order to investigate the role of hCG in the onset of human labour, uterine smooth muscles were exposed to 500 000 IU of hCG in an organ bath for 3 hours and challenged with 10 mU of syntocinon. After a period of 1 hour, another dose of 10 mU of syntocinon was added to the bath. Contractile activity (frequency × amplitude) were computed. The experiment was repeated with the addition of 10⁵ m indomethacin in the bath. Serum values of hCG from mothers in spontaneous labour at gestational ages from 34 to 42 weeks were compared. In 10 women, serum values of hCG of paired samples obtained at 34 weeks and at spontaneous onset of labour after 38 weeks were compared. 500 000 IU/l of hCG inhibits human uterine activity by 65% in vitro. The inhibitory effect was on the frequency rather than amplitude of contraction. In the presence of hCG, 10 mU/l of syntocinon was able to reinitiate normal uterine contractility, but this not in the presence of 10⁵ m indomethacin. The maternal serum concentration of hCG was lower in mothers with ongoing pregnancy compared with mothers in spontaneous labours at all gestational ages.