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Drinking alcohol during pregnancy leads to poorer cognitive functioning in children, according to the most comprehensive review on the issue to date. The University of Bristol research published today [29 January] in the International Journal of Epidemiology, reviewed 23 published studies on the topic and found evidence that drinking in pregnancy could also lead to lower birthweight. The findings reinforce the UK Chief Medical Officers' #DRYMESTER guidelines, which is abstaining from alcohol in all trimesters.

To study the effects of drinking alcohol during pregnancy, the researchers funded by the National Institute for Health Research (NIHR) and the Medical Research Council (MRC) combined results from very different study designs for the first time. Methods included traditional studies such as randomized controlled trials, alongside alternative strategies such as comparing children in the same families whose mothers cut down or increased their alcohol use between pregnancies, and a genetic marker-based approach, "Mendelian randomization."

Previously, research on this topic has been through 'observational' studies, where participants are already exposed to a risk factor and researchers do not try to change who is or isn't exposed. However, there are limitations with this type of study: it can be impossible to unpick what is caused by alcohol, and what is caused by other factors. These factors could include a woman's education or family environment, as well as genetic predisposition, which can affect her child's development and cognition in the long-term.

Alternative study designs use different ways of minimizing or removing these confounding factors, so the results are more reliable. If the results of these studies all point in the same direction, they are less likely to be because of errors and biases, and more likely to be true causes of health and disease.

All the studies included in the review tried to compare like with like groups of people who were only different in terms of exposure to alcohol during pregnancy. This is as close as it gets to what would be achieved in an experiment.

While the review was comprehensive it was limited in its ability to establish how much alcohol leads to these negative outcomes. However, the researchers concluded that women should continue to be advised to abstain from alcohol during pregnancy.

Dr. Luisa Zuccolo, the study lead and Senior Lecturer in Epidemiology at Bristol Medical School: Population Health Sciences, said: "The body of evidence for the harm that alcohol can do to children before they are born is growing, and our review is the first to look at the full range of studies on the issue. This is unlikely to be a fluke result, as we took into account a variety of approaches and results. Our work confirms the current scientific consensus: that consuming alcohol during pregnancy can affect one's child's cognitive abilities later in life, including their education. It might also lead to lower birthweight.

"Our study reinforces the UK Chief Medical Officers' guideline: DRYMESTER (abstaining in all trimesters) is the only safe approach. This message is more important than ever, given recent research which shows the alcohol industry promoting confusing information about the real health implications of drinking during pregnancy."

More information: Loubaba Mamluk et al. Evidence of detrimental effects of prenatal alcohol exposure on offspring birthweight and neurodevelopment from a systematic review of quasi-experimental studies, International Journal of Epidemiology (2020). Journal information: International Journal of Epidemiology Loubaba Mamluk et al. Evidence of detrimental effects of prenatal alcohol exposure on offspring birthweight and neurodevelopment from a systematic review of quasi-experimental studies,(2020). DOI: 10.1093/ije/dyz272