Drinking four glasses of alcoholic beverages a week can significantly reduce a woman’s chances of becoming pregnant through in vitro fertilization, a recent study conducted by researchers at the Harvard Medical School suggests. The study was headed by Dr. Brooke V. Rossi, a clinical fellow in the Department of Obstetrics, Gynecology, and Reproductive Biology at Brigham and Women’s Hospital.

Rossi and fellow researchers surveyed over 2,500 couples attempting to have a baby through IVF, comparing survey results from those couples who regularly drank alcohol to those who did not.

Rossi’s group concluded that increased alcohol consumption in both men and women strongly decreased the likelihood of a woman’s egg being successfully fertilized.

Consuming more than four drinks per week can reduce the chance of conception by 18 percent for women and 14 percent for men. In couples where both the man and woman drink up to four drinks a week, chances of conception are reduced by 26 percent—“a huge decrease,” according to Rossi.

The effects of alcohol consumption on successful pregnancy were most pronounced in women who drink four units of white wine per week and in men who drink the same amount of beer.

According to Rossi, although her research team discovered a correlation between alcohol consumption and decreased probability of pregnancy through IVF, they are still unclear about what leads to this decreased likelihood.

“This is not an epidemiologic study, so we can’t comment on what’s happening at a biological level,” Rossi said. “Based on a few animal studies, it might have something to do with the spindle of the egg.”

Though it is no surprise that alcohol consumption during pregnancy has a detrimental impact on fetal development, Rossi said she could not yet comment on the different effects alcohol has on women impregnated through in vitro versus women impregnated through sexual intercourse.

“We are now trying to analyze data to see if there are any specific differences in the cycle, egg number, sperm quality, that could contribute to these findings,” Rossi said.