Women should avoid alcohol when they are pregnant. That has been the common guidance for some time, and now a British study underscores the importance of what is known in the United Kingdom as #Drymester.

Studying women's habits when they are pregnant is tricky. Most research on the effects of prenatal alcohol exposure is done as an observational study in which investigators simply note whether participants were or were not exposed to a particular risk factor, or partake in a particular behavior.

Getting the message out about #Drymester is particularly important because the alcohol industry promotes confusing information about the health hazards associated with drinking during pregnancy.

Scientists from the University of Bristol conducted a review of the available scientific literature on prenatal exposure to alcohol, including those with study designs meant to overcome these limitations, some of which found that prenatal exposure to alcohol can harm a child’s cognitive development, the most extreme example being fetal alcohol syndrome or FAS. It can also result in low birth weight.

They analyzed data from 23 studies representing five different study designs, including randomized clinical trials and observational studies, and found strong evidence that prenatal alcohol exposure has a detrimental effect on cognitive development, and weaker evidence that it causes a decrease in birthweight. The findings reinforce the UK Chief Medical Officers’ #Drymester guidelines which recommend women abstain from alcohol throughout pregnancy.

“This is unlikely to be a fluke result, as we took into account a variety of approaches and results. Our work confirms the scientific consensus,” Luisa Zuccolo, lead author on the study, said in a statement. Getting the message out about #Drymester is particularly important because recent research shows the alcohol industry promotes confusing information about the health hazards associated with drinking during pregnancy, she added.

More studies using different analytical methods that can begin to determine how much prenatal alcohol exposure affects neurobehavioral development in babies are needed, the researchers said. Studies that take into account simultaneous and multiple sources of bias, such as genetic markers from both parents and siblings, and dose-response studies, are particularly important.

The study is published in the International Journal of Epidemiology.