Alcohol during pregnancy: drinking too much in the first week is risky

Alcohol use at any stage of pregnancy can lead to a range of consequences falling under the umbrella of fetal alcohol spectrum disorder (FASD). These consequences, ranging from mild to very severe, include birth defects, growth retardation during pregnancy and emotional and behavioural problems related to brain development.

Prenatal alcohol exposure affects an estimated 0.9 per cent of children in North America. However, it remains very difficult to diagnose after birth.

Few studies have investigated alcohol use during the preimplantation phase of embryo development, i.e., in the first week of pregnancy when the embryo is floating freely in the uterus and pregnancy tests cannot yet detect fertilization. Unborn babies are particularly vulnerable at this stage.

Until recently, it was mistakenly believed that embryos exposed to high concentrations of alcohol in this period would either undergo spontaneous abortion or develop properly. This is known as the “all-or-nothing effect.”

McGraw's work dispels this belief. 

In a 2021 study, using mice as models, his team demonstrated that embryos survive a single excessive dose of alcohol in the first week of gestation and exhibit morphological defects in 19 per cent of cases. These abnormalities, which appear early during gestation and persist over time, have also been confirmed in the current study, but represent only a small proportion of the effects of alcohol use during pregnancy.

Indeed, “in our two studies on mice models, embryos with and without morphological defects also showed abnormalities in the mechanisms controlling gene expression, particularly in genes related to brain development,” explained McGraw.

Thus, in normally developing embryos exposed to a high concentration of alcohol, it is very likely that some will have brain development issues after birth. In humans, 90 per cent of children with FASD have no physical defects, but develop intellectual, emotional or behavioural symptoms later in childhood and adolescence.

All this evidence suggests that people of childbearing age should be very cautious about drinking alcohol.

“The only way to prevent the teratogenic effects of alcohol in unborn children is to avoid drinking alcohol, but we must find other safeguards for women who don’t yet know they’re pregnant,” said McGraw.

He and his research team have shown that a diet rich in nutrients such as folic acid, vitamin B12, choline and betaine, important for the epigenetic mechanisms that control gene expression, provides some measure of protection for embryos exposed to alcohol.

In the study, mouse fetuses whose mothers were on such a diet before and during gestation had almost three times fewer morphological defects. Their skulls were closer to the expected dimensions and they had fewer and less varied morphological defects.

For McGraw, the research findings suggest that national dietary and alcohol guidelines for people of childbearing age or wishing to become pregnant should be changed.