March 23, 2000 (Atlanta) -- Mediterranean and European countries at low geog
March 23, 2000 (Atlanta) -- Mediterranean and European countries at low geographic latitudes had a higher incidence of male births in the last decade, according to a report in the Journal of Epidemiology and Community Health. Experts say this may show that temperature can influence both fertility and gender.
Because some industrialized countries have reported a decline in male births over the last 50 years, researchers explored trends on the Mediterranean island of Malta and in Western Europe. In the U.S., experts say that the sex ratio of 1.05 male births for every 1 female birth has changed little since 1950.
In Malta, the ratio of male to female births was higher than the norm and has changed little from 1890 to 1995. In Europe between 1990 and 1995, countries at latitudes of 40 to 45 degrees, which is further south, had more boy births than countries at latitudes over 55 degrees. The author says the reason for these differences is not yet known.
"We know that male fetuses are more susceptible to environmental insults and are more likely to be stillborn," says Victor Grech, MD, PhD, the pediatric senior registrar at St. Luke's Hospital in Guardamangia, Malta. "And some studies suggest that industrial byproducts may be the cause." Although there are no such byproducts in Malta, Grech tells WebMD that there may be yet another explanation.
"We speculate that temperature affects both fertility and gender," Grech tells WebMD. But he says "a true cause-and-effect relationship is a long way off. Future research is needed, from all parts of the world."
Vital Information:
- A study in Europe has shown that there is a higher incidence of male births in countries at lower latitudes.
- Researchers suspect that temperature may have an effect on both fertility and gender.
- In the U.S., the sex ratio of 1.05 male births for every 1 female birth has changed little since 1950.
