June 14, 2021 — Most women know that drinking alcohol during pregnancy can endanger the fetus before they know they’re pregnant and that there’s no established safe amount while pregnant.
What women may not know is that drinking even moderately in the middle and the latter half of the menstrual cycle may reduce the odds of successful conception.
According to a new study of drinking patterns and hormone levels at different monthly stages, moderate intake of alcohol (3-6 drinks a week) and heavy intake (more than 6 per week) during the post-ovulation phase of a woman’s cycle can disturb the delicate hormonal sequence needed to conceive. The researchers also found that heavy drinking earlier in a woman’s cycle, during ovulation, could also disrupt conception.
The message? If you want a baby, don’t wait until that much-anticipated missed period to cut back on drinking.
“The take-home message from our study is that if you want to get pregnant, don’t have more than one drink a day at any time during your menstrual cycle, and have less than half a drink during ovulation and after ovulation in the implantation period,” says lead author Kira C. Taylor, PhD, an associate professor of epidemiology and population health at the University of Louisville in Kentucky.
“Alcohol’s impact on [the likelihood of conception] has been suspected since the 1990s but has not been well-studied,” says Nishath A. Ali, MD, an assistant professor of obstetrics and gynecology at Baylor College of Medicine in Houston. “Moderate and heavy drinkers generally take longer to conceive and are at higher risk of needing an infertility evaluation,” she says.
Already, women who are having fertility treatments such as in vitro fertilization are advised to cut back on drinking.
Published June 9 in the journal Human Reproduction, the study, begun in 2017, looked at alcohol and fecundability — that is, the chance of becoming pregnant in a single menstrual cycle. It analyzed data from 413 women, ages 19 to 41, who completed daily diaries on alcohol intake, including the number of drinks and type (beer, wine, or liquor) for a maximum of 19 months of follow-up. Participants were mainly white, non-Hispanic, and married with some college education.
The women submitted monthly urine samples to assess pregnancy status, and their monthly cycle phases were calculated using a calendar-based method and compared between drinkers and nondrinkers.
During the study, 133 women became pregnant, and outcomes showed an effect of alcohol — the more alcohol a woman drank, the less chance she had of conceiving. “Among heavy drinkers, the probability of conceiving was 27.2%, rising to 41.3% in nondrinkers. Light and moderate drinkers both had about a 32% chance of conceiving,” Taylor says.
When the researchers looked at the effect of drinking alcohol during different phases of the menstrual cycle, they found that moderate and heavy drinking in the post-ovulation phase reduced the odds of conception by nearly half (44% and 49%, respectively), compared with nondrinkers. There was also some suggestion that heavy drinking before ovulation was also tied to reduced likelihood of conception.
How about binge drinking? Notably, each extra day of excessive intake over a short period was associated with a 19% reduction in conception around the time of ovulation and between ovulation and menstruation. But it didn’t seem to have an effect early in the cycle, before ovulation.
The researchers also found that the type of alcoholic beverage didn’t change the results.
“In addition, the study showed that the menstrual cycle lengths were the same for women in every drinking category, suggesting that drinking did not affect the hormones that regulate the length of the cycle,” says Christine Metz, PhD, a professor at the Feinstein Institutes for Medical Research in Manhasset, NY.
The authors think that part of the alcohol-conception connection may be disruptive changes in steroid hormones, particularly a surge in estradiol, a form of estrogen
“The increase in estrogen can result in irregular cycles, delayed ovulation, or anovulation. So couples could be trying to get pregnant at the wrong time in terms of ovulation,” Taylor says. “An increase in estrogen can also impact the timing of the window of opportunity in the lining of the uterus for implantation after fertilization.”
Experts are not exactly sure how a badly timed spike in estradiol might affect the odds of conception. While this is not clearly understood, it seems that the timing of heavy drinking may not only suppress ovulation, but may also suppress the ability to sustain an early pregnancy, notes Ali.
And men aren’t off the hook either — their testicles can also be affected by drinking. “Heavy alcohol consumption is associated with abnormalities in gonadal function in men, including a reduction in serum testosterone and decreased sperm counts,” Ali says.
One caution about the new data, the authors say, is that only 20% to 25% of women across the study’s groups were actually trying for a pregnancy, while ideally such a study should include only women intending to conceive.
Also, the study didn’t look at the influence of male partners’ drinking, and the data relied on self-reporting by participants, which depends on accurate recollection. Still, the study points to one more compelling reason to cut back on alcohol before you start trying to conceive.
The bottom line, says Ali: “Lifestyle interventions are important for both members of a couple planning a pregnancy.”
Human Reproduction: “The association between alcohol intake and fecundability during menstrual cycle phases.”
Kira C. Taylor, PhD, associate professor of epidemiology and population health, University of Louisville, Kentucky.
Nishath A. Ali, MD, assistant professor of obstetrics and gynecology, Baylor College of Medicine, Houston..
Christine Metz, PhD, professor, Feinstein Institutes for Medical Research, Manhasset, NY.
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