Lead author Ellen Mikkelsen, of Aarhus University Hospital in Denmark, said: "For many women of reproductive age, alcohol consumption is an integral part of their lifestyle. In this prospective study of women trying to conceive, consumption of the highest amount of alcohol was associated with a decrease in fecundability [probability of being able to conceive] compared with no alcohol consumption."
The level at which it begins to impact upon fertility is around 16 units a week, where a unit is the equivalent of around 87ml of wine.
However, there was no impact for women who drank less.
Experts in Britain said the study showed that drinking occasionally was unlikely to impact on pregnancy.
Annie Britton, from University College London, said the results offer reassurances to couples trying to get pregnant and suggests that "total abstinence may not be necessary to maximise conception rates" because "if alcohol is consumed moderately, it seems that this may not affect fertility".
"It would be wise to avoid binge drinking, both for the potential disruption to menstrual cycles and also for the potential harm to a baby during early pregnancy," she added.
"If a couple are experiencing difficulty in conceiving, it makes sense for both partners to cut down on their alcohol intake."
The research was published in the BMJ.