Israeli scientists have demonstrated that levels of maternal serum HCG (MSHCG) the hormone that reveals in blood or urine tests whether or not a woman is pregnant are nearly a fifth higher less than three weeks into pregnancy if a woman is carrying a girl than if she is carrying a boy.
HCGs role at the beginning of pregnancy is to maintain the function of the corpus luteum a temporary structure formed in the ovary after an egg is shed that produces oestrogen and progesterone until the placenta can take over their production.
"Other research has already shown that MSHCG is significantly higher in the presence of a female fetus in the second and third trimesters of pregnancy. But weve discovered that levels were increased as early as 16 days after fertilisation," said lead researcher, Dr Yuval Yaron, Director of the Prenatal Genetic Diagnosis Unit in the Genetic Institute at Tel Aviv Medical Center.
He said that their finding that MSHCG levels increase with female fetuses before the development of the glands that produce the fetal hormones means that the higher level must be due to the way that the placenta expresses proteins in female pregnancies and not to male hormones suppressing MSHCG, as has been suggested by other researchers. Genes that the researchers believe are potential candidates for regulating protein expression in the placenta have been mapped to the X (female) chromosome.
The study involved 347 IVF pregnancies with women being measured for MSHCG levels between one and three times from day 14 to day 20. There were 184 female fetuses and 163 male fetuses. MSCHG levels were 18.5% higher by three weeks gestat
'"/>
Contact: Margaret Willson
m.willson@mwcommunications.org.uk
44-01-536-772-181
European Society for Human Reproduction and Embryology
29-Jan-2002