Higher alcohol consumption impacts on ability to conceive

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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%. 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 Gynaecologists 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 a British medical journal 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, at the department of clinical epidemiology, Aarhus University Hospital and 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 foetus.”

Objective: To investigate to what extent alcohol consumption affects female fecundability.
Design: Prospective cohort study.
Setting: Denmark, 1 June 2007 to 5 January 2016.
Participants: 6120 female Danish residents, aged 21-45 years, in a stable relationship with a male partner, who were trying to conceive and not receiving fertility treatment.
Main outcome measures: 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 categorized in standard servings per week (none, 1-3, 4-7, 8-13, and ≥14). Participants contributed menstrual cycles at risk until the report of pregnancy, start of fertility treatment, loss to follow-up, or end of observation (maximum 12 menstrual cycles). A proportional probability regression model was used to estimate fecundability ratios (cycle specific probability of conception among exposed women divided by that among unexposed women).
Results: 4210 (69%) participants achieved a pregnancy during follow-up. Median alcohol intake was 2.0 (interquartile range 0-3.5) servings per week. Compared with no alcohol consumption, the adjusted fecundability ratios for alcohol consumption of 1-3, 4-7, 8-13, and 14 or more servings per week were 0.97 (95% confidence interval 0.91 to 1.03), 1.01 (0.93 to 1.10), 1.01 (0.87 to 1.16) and 0.82 (0.60 to 1.12), respectively. Compared with no alcohol intake, the adjusted fecundability ratios for women who consumed only wine (≥3 servings), beer (≥3 servings), or spirits (≥2 servings) were 1.05 (0.91 to1.21), 0.92 (0.65 to 1.29), and 0.85 (0.61 to 1.17), respectively. The data did not distinguish between regular and binge drinking, which may be important if large amounts of alcohol are consumed during the fertile window.
Conclusion: Consumption of less than 14 servings of alcohol per week seemed to have no discernible effect on fertility. No appreciable difference in fecundability was observed by level of consumption of beer and wine.

Ellen M Mikkelsen, Anders H Riis, Lauren A Wise, Elizabeth E Hatch, Kenneth J Rothman, Heidi T Cueto,Henrik Toft Sørensen

Broadly-Vice.com material
BMJ abstract
BMJ editorial

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