Temporal relationship between the human chorionic gonadotrophin peak and the establishment of intervillous blood flow in early pregnancy.

The purpose of this study was to investigate the temporal relationship between the early pregnancy peak of circulating human chorionic gonadotrophin (HCG) concentration and the establishment of maternal blood flow in the placental intervillous space. The presence of blood flow echoes within intervillous space was determined by colour Doppler imaging from 44 women with clinically uncomplicated pregnancy between 6 and 18 weeks gestation. Circulating HCG, free alpha- and beta HCG subunits, oestradiol and progesterone concentrations were immunoassayed in blood samples collected at the time of Doppler examination. A continuous intervillous blood flow was detected in all cases with a gestational age > or = 11.7 weeks (n = 18) but never before this time. Circulating concentrations of free alpha HCG, oestradiol and progesterone were linearly or exponentially correlated with gestational age (r = 0.860, 0.903 and 0.538 respectively, all with P < 0.001), indicating steady increase of these hormones with advancing gestation. However, the best fitted lines were found to be parabolic for HCG (r = 0.771, P < 0.001) and beta HCG (r = 0.695, P < 0.001), their highest points corresponding to 11.24 and 10.74 weeks gestational age respectively. The close temporal relationship between the Doppler advent of intervillous maternal blood flow and the HCG peak suggests that the establishment of the intervillous blood flow is associated with the decline in circulating HCG concentrations.