Pregnancy health centre

Drinking in early pregnancy most likely to affect baby

By Sophie Ramsey

BMJ Group News

What do we know already?

When a pregnant woman drinks alcohol, it passes to her developing baby through the placenta. The baby can’t break down alcohol as quickly as an adult would, so it stays in the body longer.

This can lead to a wide range of problems, including a low birth weight and length; learning, behavioural, and thinking (cognitive) difficulties; and defects involving the heart and other organs. If these problems are severe, they are known as fetal alcohol syndrome. Alcohol can also affect a baby’s appearance, causing a smaller-than-usual head (microcephaly), no groove between the nose and upper lip (a smooth philtrum), a thin upper lip, and small eyelid openings.

The connection between alcohol and these problems is well-established, and alcohol is thought to be particularly harmful during the first trimester. However, not much is known about exactly when alcohol is most likely to cause each of these problems in pregnancy.

In the new study, researchers interviewed 922 women throughout their pregnancy about how much they drank. After they gave birth, an expert on physical defects examined their baby. The researchers also recorded the babies’ birth weight and length, and head measurement.

What does the new study say?

There was no stage of pregnancy where drinking alcohol was safe, and no safe amount of alcohol to drink. But the chance of the baby having problems was higher at certain times, and with more alcohol. For example, 9 in 100 babies born to women who averaged one or more drinks a day in the first trimester were born with a smooth philtrum. This dropped to 2 in 100 babies born to women who averaged less than one drink a day.

Drinking between the sixth and 12th weeks of pregnancy carried the highest risk of problems. For every one-drink increase in the average amount consumed daily, the risk climbed 25 percent for a smooth philtrum, 22 percent for a thin upper lip, 12 percent for microcephaly, 16 percent for a low birth weight, and 18 percent for a reduced birth length. The researchers found similar increases with each additional episode of binge drinking (consuming a high amount of alcohol at one time).

Drinking in the second trimester (weeks 12 to 24) also carried a higher risk of a smooth philtrum and a low birth weight and length. And drinking in the final trimester was linked to a smaller birth length.

One drink was roughly the equivalent of a small (less than 125ml) glass of wine, a large shot of spirits or half a pint of beer.

How reliable is the research?

These findings should be fairly reliable, as this was a well-designed and carefully conducted study.

The researchers took into account other factors that might have affected the risk of problems, such as the women’s ages, whether they smoked and whether they took any medicines or illegal drugs while pregnant.

The researchers also interviewed the women about their drinking habits throughout their pregnancy, rather than asking them to remember how much they drank later on. Even so, we can’t be certain that the women accurately remembered or were truthful about how much they drank.