Researchers from University College London carried out a large study to examine the association between pre-conception alcohol consumption and time to pregnancy.
In total, 6,120 female Danish residents, aged 21-45 years, were included in the study. They were all in a stable relationship with a male partner, trying to conceive and not receiving fertility treatment, between 2007-2016.
Each female participant completed bimonthly questionnaires for 12 months, or until conception occurred, on alcohol use, pregnancy status, menstrual cycles, frequency of intercourse and smoking.
Alcohol consumption was self reported as beer (330 mL bottles), red or white wine (120 mL glasses), dessert wine (50 mL glasses) and spirits (20 mL), and was categorised in standard servings per week.
In women who drank 14 or more servings of alcohol a week, there were 37 pregnancies in 307 cycles, compared with 1,381 pregnancies in 8,054 cycles in women who did not drink.
Women who drank more than 14 servings a week had an 18 per cent lower chance of getting pregnant, according to the 'BBC'.
While the sample size was large, only 1.2 per cent of women drank more than 14 servings of alcohol a week, so the estimate for this high level of exposure is imprecise, researchers said.
This is an observational study, so no firm conclusions can be made about cause and effect, they said.
The study did not distinguish between regular and binge drinking, which is important because alcohol can affect the menstrual cycle.
The researchers recommend couples to abstain from alcohol during fertile window until a pregnancy is ruled out, because the foetus may be particularly vulnerable to alcohol during the first few weeks after conception.
Although the study suggests that low to moderate intake of alcohol, defined as one to seven servings a week, seemed to have no effect on women's fertility, nor did the type of alcohol beverage consumed.
In developed countries, up to 24 per cent of couples experience infertility, defined as time to pregnancy of 12 months or more.
Annie Britton from University College London, said the results "offer some reassurances" to couples trying to get pregnant.
It also 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," added Britton.
"If a couple are experiencing difficulty in conceiving, it makes sense for both partners to cut down on their alcohol intake," she added.
The study appears in The BMJ Journal.