Couples who share a bottle of wine a week reduce their chances of having a baby through IVF by more than a quarter, according to a study by American fertility specialists.
Research into alcohol consumption among couples being treated at a fertility clinic found fewer successful pregnancies when the women drank several glasses of wine a week, or the man had a daily beer.
Doctors at Harvard medical school, in Boston, asked 2,574 couples about their drinking habits shortly before they embarked on a course of IVF treatment.
A little over half of the women (56%) and a third of the men had less than one alcoholic drink a week, while 4% of women and 5% of men consumed at least one drink every day.
Dr Brooke Rossi, who led the study, said men and women who each drank six units of alcohol a week each or more "significantly reduced their likelihood of pregnancy".
At these levels of consumption, women were 18% less likely to have a successful IVF baby, while men reduced their chances of fatherhood by 14%.
The effects were particularly strong for women who drank white wine and men who preferred drinking beer, Rossi told the American Society of Reproductive Medicine annual meeting in Atlanta, Georgia last month.
"In general, women are told they should stop drinking when they are trying to achieve pregnancy," Rossi said. The men and women who took part in the study had average ages of 37 and 34 respectively. They were all from the Boston area and completed questionnaires about their drinking habits between 1994 and 2003.
Tony Rutherford, chairman of the British Fertility Society, said guidelines from the society and the National Institute for Health and Clinical Excellence (Nice) advise women to stop drinking completely throughout their pregnancy. "The link between alcohol and conception is an area where the evidence is not clear-cut. It may well be that couples who are already subfertile are more affected by alcohol that those who are perfectly fertile," he said
"If you are going to have IVF, my recommendation would be that it makes sense to avoid alcohol all together, from three months beforehand."
A previous study, published in the British Medical Journal by Tina Jensen at the National University hospital in Copenhagen, Denmark, found that women were less likely to conceive if they drank moderately.
But other studies have found that alcohol had little effect on the time it took women to conceive.
Rutherford added: "This is further evidence to suggest that alcohol does have an impact and that those women who try for a baby should think about their lifestyle choices.
"Eggs and sperm take at least three months to develop so women have got to stop smoking, reduce alcohol consumption or, if you are overweight, correct that weight, that far ahead if you want to maximise your chances of conception."
