The story of alcohol and accidental pregnancy goes back to time immemorial. Long before Knocked Up, Neanderthal woman almost certainly found herself impregnated by a total loser as a result of too much grog around the campfire. But while many of us associate too much booze with ripped condoms and missed periods, new research suggests that alcohol might not be the baby-maker of popular repute.
Researchers in Denmark have conducted one of the world's first mass-scale studies into how alcohol consumption affects your ability to get pregnant. They surveyed 6,120 Danish women aged 21 to 45 in relationships with male partners and were trying to get pregnant, asking them to monitor and log their alcohol intake using online questionnaires.
The Danish team found that women who drank less than 14 servings of alcohol a week suffered no discernible effect on their fertility. (One serving of booze was defined as containing 12 grams of alcohol.) However, women drinking more than 14 or more servings a week—equivalent to just over two bottles of wine over the course of seven days—found that their chance of getting pregnant fell by about 18 percent. One in five women in this drinking category failed to get pregnant.
While the guidance on alcohol consumption for women seeking to conceive varies from country to country, US health authorities advise women to abstain entirely if they are looking to conceive. According to the Centre for Disease Control and Prevention, "there is no known safe amount of alcohol use during pregnancy or while trying to get pregnant." The American College of Obstetricians and Gynecologists agrees: "Women should avoid alcohol entirely while pregnant or trying to conceive because damage can occur in the earliest weeks of pregnancy, even before a woman knows that she is pregnant."
Some scientists believe the US approach is unnecessarily restrictive. A recent editorial in British medical journal BMJ argues that women trying to get pregnant should cut back on their alcohol use, but that abstinence isn't necessary—a recommendation in line with the Danish study.
"There have been very few studies of women trying to get pregnant," explains Ellen M Mikkelsen, the lead researcher on the study, "because most studies are retrospective—as in, asking women who have become pregnant about their behavior before they conceived." She highlights that recall bias can influence such studies: "It's difficult to remember accurately how much alcohol you were consuming when you were trying to become pregnant."
All the women in her study were self-selected, volunteering to help after responding to online adverts seeking participants. The respondents then filled out online questionnaires reporting their alcohol consumption every eight weeks. I ask how she could be sure they weren't under-reporting the amount they were drinking.
"We can never know for sure," she replies. To counteract this effect, the researchers looked for scientific parallels. "We know that women often under-report their weight and over-report their height. We validated our findings against a registered database, and it seems like Danish women are generally quite honest."
Unlike the US advice on drinking when looking to conceive, Mikkelsen team observed no fertility problems for women who drank less than 14 units a week. While more research is needed to explain why alcohol impacts fertility in this way, Mikkelsen believes it might be due to hormonal changes.
In future, she also hopes to expand upon her findings to find out whether booze makes sperm swim less effectively. "We've added one piece to the puzzle to explain why certain factors affect fertility. The next thing we're hoping for is to have enough males enrolled in our study so we can add male alcohol consumption to the study and see if that also has an effect."
While the findings may be good news for moderate winos looking to get pregnant, Mikkelsen urges women not to throw caution to the wind entirely. "I'm not advising women who are trying to conceive to drink. Alcohol might have other negative effects, and if you don't know you're pregnant, alcohol can affect the fetus."