University of Louisville School of Public Health and Information Sciences researcher Kira Taylor and her team analyzed data from more than 400 women for up to 19 months. The women completed daily diaries reporting how much alcohol they drank and what type.

Heavy drinking was defined as more than six alcoholic drinks a week, moderate drinking was three to six drinks a week, and binge drinking was defined as four or more drinks on a single day. A drink was defined as a third of a liter of beer, a medium glass of wine or just under a double shot of spirits. The researchers collected information on factors that could affect the results, such as age, medical history, smoking, obesity, intercourse frequency, use of birth control methods and intention to become pregnant.

“We found that heavy drinking during any phase of the menstrual cycle was significantly associated with a reduced probability of conception compared to non-drinkers,” Taylor said. “This is important because some women who are trying to conceive might believe it is ‘safe’ to drink during certain parts of the menstrual cycle.”

The research also found during the luteal phase, or the last two weeks of the menstrual cycle before bleeding starts and when the process of implantation occurs, not only heavy drinking but also moderate drinking was significantly associated with a reduced probability of conception. At the time of ovulation, usually around day 14 of the cycle, consuming a lot of alcohol – either heavy or binge drinking – was significantly associated with reduced chances of conception.

“If we assume that a typical, healthy, non-drinking woman in the general population who is trying to conceive has approximately a 25% chance of conceiving during one menstrual cycle, then out of 100 women approximately 25 non-drinkers would conceive in a particular cycle, about 20 moderate drinkers would conceive and only about 11 heavy drinkers would conceive,” Taylor said. “But the effect of moderate drinking during the luteal phase is more pronounced and only about 16 moderate drinkers would conceive.

“Our study only included a few hundred women and, while we believe the results strongly suggest that heavy and even moderate alcohol intake affects the ability to conceive, the exact percentages and numbers should be viewed as rough estimates,” she said.

Each extra day of binge drinking was associated with an approximate 19% reduction in the odds of conceiving during the luteal phase and a 41% reduction during the ovulatory phase. The researchers found no difference in their results between different types of drinks. The influence of drinking by male partners was not assessed.

While the study does not show that drinking alcohol causes the reduction in the chances of becoming pregnant, it does point to an association. Possible biological mechanisms to explain the association could be that alcohol intake affects the processes involved in ovulation so that no egg is released during the ovulatory part of the cycle, and alcohol could affect the ability of a fertilized egg to implant in the womb.

“The results in this study should not be construed to mean that drinking alcohol prevents pregnancy. In other words, alcohol is not birth control. Even if a woman drinks alcohol heavily, if she has unprotected intercourse, she can become pregnant,” Taylor said.

University of Louisville School of Public Health and Information Sciences epidemiologist Kira Taylor, PhD, and her UofL and Emory University colleagues, found that women who reported feeling more stressed during their ovulatory window were approximately 40-percent less likely to conceive during that month than during other, less stressful months. Similarly, women who generally reported feeling more stressed than other women were about 45-percent less likely to conceive. The results of the study were recently published in the journal .

In the study, 400 women 40-years-old and younger who were sexually active recorded their daily stress levels measured on a scale from one to four (low to high). The diaries also contained information regarding menstruation, intercourse, contraception, alcohol, caffeine and smoking. Urine samples also were collected throughout the study, and women were followed until they became pregnant or until the study ended, for an average of eight menstrual cycles.

Researchers calculated mean stress levels during each phase of the menstrual cycle, with day 14 as the estimated time of ovulation. They found the negative effect of stress on fertility was only observed during the ovulatory window, and was true after adjustments for other factors such as age, body mass index, alcohol use and frequency of intercourse.

“These findings add more evidence to a very limited body of research investigating whether perceived stress can affect fertility,” Taylor said. “The results imply that women who wish to conceive may increase their chances by taking active steps towards stress reduction such as exercising, enrolling in a stress management program or talking to a health professional.”

The study also found that women who did conceive experienced an increase in stress at the end of the month in which they became pregnant. Taylor hypothesizes this could be the result of two factors: women became stressed after taking a home pregnancy test and learning they were pregnant, and/or most likely the increased stress was the result of changes in hormone levels caused by pregnancy itself.

“Some individuals are skeptical that emotional and psychological attributes may be instrumental in affecting fertility,” Taylor said. “I hope the results of this study serve a wake-up call for both physicians and the general public that psychological health and well-being is just as important as other more commonly accepted risk factors such as smoking, drinking alcohol, or obesity when trying to conceive.”