Different maternal serum hCG levels in pregnant women with female and male fetuses: does fetal hypophyseal--adrenal--gonadal axis play a role?

Fetal gender has a significant effect on maternal and cord blood hCG levels, particularly during the last trimester of the pregnancy. However, the reason for this difference is obscure. The aim of the present study was to investigate whether term fetal hypophyseal - adrenal - gonadal axis differs between female and male fetuses thereby causing different hCG levels. The study consisted of 60 women with singleton pregnancies in the third trimester. Thirty-one pregnant women were carrying female fetuses, whereas 29 were carrying male. Human chorionic gonadotropin (hCG), estradiol, progesterone, testosterone, dehydro-epiandrosteron-sulfate (DHEAS), prolactin and growth hormone levels were measured in maternal serum and umbilical cord blood. In female bearing pregnancies maternal and cord blood hCG levels were significantly higher than in male bearing pregnancies (P<0.001). Maternal and cord blood estradiol, progesterone, testosterone, DHEAS, prolactin and growth hormone levels were not significantly different in either fetal gender. When all patients were considered as a group there were no correlations between fetal hCG levels and any of the measured hormones. Term fetal DHEAS, estrogen, progesterone, testosterone, growth hormone and prolactin levels do not contribute to different hCG levels between female and male fetuses. It is possible that fetal hypophyseal-adrenal gonadal axis does not play a central role as the cause of different hCG levels.