Pregnancy: 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 relationshipbetween the early pregnancy peak of circulating human chorionicgonadotrophin (HCG) concentration and the establishment of maternalblood flow in the placental intervillous space. The presenceof blood flow echoes within intervillous space was determinedby colour Doppler imaging from 44 women with clinically uncomplicatedpregnancy between 6 and 18 weeks gestation. Circulating HCG,free - and HCG subunits, oestradiol and progesterone concentrationswere immunoassayed in blood samples collected at the time ofDoppler examination. A continuous intervillous blood flow wasdetected in all cases with a gestational age 11.7 weeks (n =18) but never before this time. Circulating concentrations offree HCG, oestradiol and progesterone were linearly or exponentiallycorrelated with gestational age (r = 0.860, 0.903 and 0.538respectively, all with P < 0.001), indicating steady increaseof these hormones with advancing gestation. However, the bestfitted lines were found to be parabolic for HCG (r = 0.771,P < 0.001) and HCG (r = 0.695, P < 0.001), their highestpoints corresponding to 11.24 and 10.74 weeks gestational agerespectively. The close temporal relationship between the Doppleradvent of intervillous maternal blood flow and the HCG peaksuggests that the establishment of the intervillous blood flowis associated with the decline in circulating HCG concentrations.