TUESDAY, Jan. 29, 2002 (HealthDayNews) -- Levels of a key maternal hormone during the first month of pregnancy may signal whether the developing fetus is a boy or girl, a new study suggests.
Israeli researchers say that even at three weeks after fertilization, mothers carrying girls have a nearly 20 percent higher concentration of the hormone, called human chorionic gonadotropin (HCG), in their blood than those bearing boys. The scientists caution that HCG levels vary too much between individuals to be a useful predictor of gender so soon in gestation -- at least for now. However, they say, the finding does show such a test may become viable if other early markers of gender identity are discovered.
The ability to know a baby's sex before it's a month old may strike some parents as unnecessary, and even morally suspect if it tempts people to select the sex of their unborn child through abortion. Yet the researchers say their work could let doctors identify fetuses with serious sex-linked genetic diseases such as hemophilia and Duchenne muscular dystrophy.
A report on their findings appears in tomorrow's issue of Human Reproduction, a European fertility journal.
HCG supports a temporary structure in the ovary called the corpus luteum, which after shedding an egg produces the hormone progesterone until the placenta is able to do so on its own.
The presence of HCG in either blood or urine is a nearly perfect indicator of pregnancy, so doctors look for it in women with a positive result on a take-home pregnancy test. They also measure HCG over time to make sure pregnancies are progressing healthily, since the hormone is supposed to increase as gestation proceeds.
Earlier research showed a woman's HCG concentration is higher when she's carrying a female fetus than it is when her baby is a boy, and this difference appears late in the first trimester. Some scientists have proposed the split occurs because male fetuses start suppressing maternal HCG.
In the new work, Dr. Yuval Yaron, of Sourasky Medical Center in Tel Aviv, and his colleagues sought to learn how soon after fertilization they could detect maternal HCG's link to gender. The researchers collected blood from 335 women (who had a total of 347 pregnancies) undergoing fertility treatments and analyzed samples from the subjects who went on to have a successful singleton delivery. Of those babies, 184 were girls and 163 were boys.
Yaron's group measured HCG levels between days 14 and 20 after fertilization, and found they could detect more of the hormone in the pregnancies that turned out to be female, starting on the 16th day. By three weeks into gestation, maternal HCG was about 19 percent higher, on average, for girls than boys, they say.
Three weeks into pregnancy is too early for the fetus to be secreting detectable levels of hormones, Yaron's group says. So, the difference must be coming from the placenta and regulated by the way that membrane responds to its female cargo.
"Although the gender differences are statistically significant, the proportion of pregnant women with serum HCG concentrations high or low enough to allow a prediction with high probability is too small," Yaron says in a statement. "It would be possible to predict the sex of a fetus if we can identify other markers that also demonstrate early gender-related differences. We are working on this now, and hope to have some results soon."
Yaron's group says such a test would be useful for parents with a family history of genetic diseases linked to the two sex chromosomes, X and Y.
Dr. Paul G. McDonough, a reproductive endocrinologist at the Medical College of Georgia in Augusta, agrees that identifying fetuses with these afflictions early in development might be appealing. However, he worries that, for most people, the real attraction of gender-typing tests is impatience. And for researchers, the allure of developing the earliest predictor possible is often commercial.
"Everybody's out there fishing for that kind of thing," he says.
Beyond that complaint, McDonough says the latest study may not show what it purports. The researchers collected one to three samples from each women, meaning that one subject with three extremely high HCG levels could have thrown off the analysis. He also points out that all of the women were seeking in vitro fertilization, and by definition had abnormal reproductive capacity. "If one were really ever to design a study like this you would want to take pregnancies" from normal women, he says.
What To Do
To read more about HCG, check out the InterNational Council on Infertility Information Dissemination.
For more on sex-linked diseases, try the Howard Hughes Medical Institute.
