Correlation between fetal sex and human chorionic gonadotropin in peripheral maternal blood and amniotic fluid in second and third trimester normal pregnancies

Background To study the correlation between fetal sex and human chorionic g onadotropin (hCG) in maternal blood and amniotic fluid. Method and material. One hundred and thirty uncomplicated pregnancies, 82 o f whom were at sixteen and 48 at thirty-five weeks of gestation. Results. The hCG levels were significantly higher in maternal serum than in amniotic fluid. At 16 weeks there were no sex-related differences in the h CG levels, either in maternal blood or in amniotic fluid. At 35 weeks the h CG levels in maternal blood were significantly higher in pregnancies with f emale fetuses than in those carrying male fetuses (p<0.004), while in amnio tic fluid the hCG levels tended to be slightly higher in the female group t han in the male. In pregnancies with female Fetuses the hCG levels in mater nal blood were significantly higher at 35 than at 16 weeks (p<0.02), while in pregnancies with male fetuses the levels were highest at 16 weeks. For b oth sexes the hCG levels in amniotic fluid were significantly higher at 16 than at 35 weeks of pregnancy (p<0.001). Whereas a significant correlation between hCG levels in maternal blood and amniotic fluid was seen at 16 week s of gestation for both sexes (p<0.01 and R value 0.45 for males and 0.41 f or females), no correlation was observed at 35 weeks. Conclusion. This study shows a significant correlation between hCG and Peta l sex at third trimester of gestation only, possibly caused by a gender fac tor and a shift in synthesis and/or in metabolism of hCG from the second to the third trimester.