“Pregnant women who drink alcohol may reduce sperm count of sons,” according to The Guardian . It reported that research has found that pregnant women who drank more than 4.5 alcoholic drinks a week were more likely to have sons who had a lower sperm count than women who drank little alcohol.
This Danish research has analysed the pregnancy drinking habits of 347 women during pregnancy and the quality of their adult sons’ semen. Although the study found a relationship between higher alcohol consumption and lower sperm concentration, semen volume and total sperm count, the trend and its implications are not completely clear. There are numerous limitations to the research, such as the small number of participants and the adaptation of a study design originally devised to examine smoking. Crucially though, male fertility was not directly assessed, meaning it is incorrect to assume that the men involved would have difficulties if they try to father children.
Overall, there are no definite conclusions to draw from this limited research. However, regardless of the study’s limitations, pregnant women are strongly advised to limit or avoid alcohol during pregnancy due to the numerous established harmful effects of excess alcohol during pregnancy.
The study was carried out by researchers from Aarhus University Hospital, Denmark, and funded by Danish Medical Research Council. The study was published in the peer-reviewed medical journal, Human Reproduction.
News reports have reflected the findings of this research, but have generally not taken into account several of the study’s important limitations. This means that no firm conclusions can be drawn on this issue. The Daily Mail ’s opening paragraph, which says that ‘pregnant women who drink alcohol could be jeopardising their chances of becoming grandmothers,’ is not substantiated by this research or supported by the researchers.
This was a cohort study that aimed to investigate the effects of exposing a male foetus to alcohol. Specifically, it looked at what effect maternal alcohol consumption during pregnancy has upon sperm quality and levels of reproductive hormones once the child has reached adulthood.
A cohort study is the best design for examining the relationship between a cause (maternal alcohol) and potential effect (reduced fertility in the son). However, to ensure the accuracy of its results a cohort study must take into account all possible confounders that could affect the relationship being studies. A limitation of this particular study is that it was not set up to examine the link between maternal alcohol consumption during pregnancy and sperm quality in the son. The original aim and design was an examination of the effect of smoking in pregnancy on sperm quality.
This research used participants of a Danish cohort study (the Healthy Habits for Two study), which recruited 11,980 pregnant women between 1984 and 1987. At 36 weeks of pregnancy the women completed a questionnaire on their lifestyle habits including drinking of beer, wine and spirits. Responses were categorised as drinks per week (for each drink type): never, 1, 1-4, 5-9, 10-14, 15-19, 20 or more.
After summing the total of each type of drink, they put each woman into a category of: less than one drink a week, one to 1.5 drinks a week, two to four drinks, or 4.5 or more drinks a week. One standard drink in Denmark reportedly corresponded to 12g of pure alcohol. In the UK, one standard drink (unit) contains 8g of pure alcohol.
In 2004, a total of 5,109 sons were identified through the Danish Civil Registration System. Between 2005 and 2006, the researchers collected semen samples from 347 men (48.5% of the 716 invited to participate) and took blood samples (both performed with due laboratory protocols). They analysed semen for sperm concentration and motility, and looked at hormone concentrations in the sample.
The men also provided questionnaires containing health and lifestyle questions, including about their own alcohol consumption. When calculating the associations between maternal alcohol and semen quality the researchers adjusted for maternal smoking, and in the sperm donor’s, smoking, alcohol, history of reproduction infections/disease, and days of sexual abstinence prior to providing the sample.
Of the mothers of the 347 men who participated in the study, 110 drank less than one drink a week during pregnancy, 127 had one to 1.5 drinks a week, 72 women had two to four drinks a week, and 38 drank 4.5 or more drinks a week.
There was a trend for decreasing sperm concentration with increasing alcohol exposure while in the uterus. The researchers calculated that sons of mothers who were in the highest alcohol category during pregnancy (more than 4.5 drinks a week) had a 32% lower sperm concentration than those whose mothers were in the lowest category (less than one drink a week).
Maternal alcohol consumption showed no clear relationship with either semen volume or total sperm count (the 1-1.5 drinks per week group was associated with the highest volume and sperm count). There was no observed association between maternal alcohol consumption and hormone levels, sperm motility or sperm morphology. They also found that higher pregnancy alcohol consumption was independently associated with the mum being of lower BMI, being of older age and being a smoker, and with the son being of lower birth weight.
The researchers conclude that their results indicate that prenatal exposure to alcohol may have an adverse effect on sperm production, and if this were a causal relationship it could explain some of the reported differences in semen quality between populations and across generations.
This research has found some association between semen quality in sons and their mothers’ alcohol consumption during pregnancy. However, there are several important limitations to this research:
Regardless of the limitations of this research and uncertainty over its findings, there are numerous other established harmful effects of consuming alcohol during pregnancy. NICE recommendations on alcohol consumption (based on one unit being 8g of pure alcohol instead of the 12g used in this study) during pregnancy advise that: