Deciding whether to drink alcohol during pregnancy is a confusing business. Anecdotally, viewpoints on the matter range from testimonies of “I drank through the whole of my pregnancy and my child turned out fine” to reports of bartenders refusing to serve alcohol to pregnant women. Recommended guidelines from health professionals are highly variable, with some doctors recommending complete abstinence and others suggesting that occasional light drinking is unlikely to cause harm to the baby.

The evidence base for the detrimental effects of alcohol abuse during pregnancy is well established, but less is known about the impact of light or heavy social drinking in pregnancy. This week, a new study published in the journal of European Child and Adolescent Psychiatry found evidence that drinking during pregnancy might be a risk factor for later childhood problems. It therefore seems timely to ask, when it comes to social alcohol use in pregnancy, how much is too much?

Guidelines

The Department of Health (DoH) recommends that healthy (non-pregnant) adults do not regularly exceed 2-3 units of alcohol per day for women and 3-4 units per day for men. Alcohol use above these guidelines is associated with increased risk for disorders including cancer and heart disease. When it comes to drinking during pregnancy, similar guidelines have been recommended by relevant health bodies. The DoH, the National Institute for Health and Care Excellence (Nice) and the Royal College of Obstetricians & Gynaecologists (RCOG) all recommend that the safest option is for women to not drink at all during pregnancy. Nice advises women to abstain from drinking in the first trimester of pregnancy to reduce risk of miscarriage and the RCOG states that small amounts of alcohol (no more than 1-2 units once or twice a week) have not been shown to be harmful. But what does the evidence say?

Research evidence

There is a large body of research exploring the effects of prenatal alcohol abuse on the foetus and newborn baby. Less reported is the long-term impact of social alcohol use during pregnancy.

The most effective way of assessing the long-term effects of drinking during pregnancy is to follow the mother and child across their lives (longitudinal research), taking measures (eg weight, behaviour problems, parent and teaching reports) at various time points. This type of research is extremely costly and families can be difficult to follow if they move house or change their mind about taking part in the study. However, there is an emerging body of longitudinal research studying the effects of prenatal alcohol intake.

One study conducted in South Africa examined the effects of prenatal alcohol consumption in women defined as either heavy drinkers (two or more drinks per day or four or more drinks on one occasion) or light drinkers (less than one drink a day or abstinent) on physical growth. Child weight, height and head circumference were measured at birth, and at five and nine years old. Findings showed that children with mothers who drank heavily had lower weight, height and head circumference from birth through to nine years.

Head circumference is an indicator of brain development. Therefore prenatal alcohol use of two or more drinks per day or four or more drinks on one occasion is a potential risk factor for persistent cognitive and behavioural impairment and mental health problems.

The study published last week examined the effects of binge drinking during pregnancy on mental health and academic performance in children aged 11. The study used data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to explore associations between episodes of binge drinking (four or more alcoholic drinks per day) and parent and teaching ratings of the child’s mental health and academic performance (assessed by examination results).

The study showed that drinking four or more drinks, at least once during pregnancy, was associated with higher levels of parental-reported mental health problems at age 11, in particular problems with hyperactivity and attention in girls. After separating the effects of binge episodes and daily drinking, binge episodes (four or more alcoholic drinks per day) were independently associated with teacher-reported hyperactivity and inattention for girls and boys. These data suggest that occasional binge drinking during pregnancy is a risk factor for child mental health problems and poor academic performance, even if daily use of alcohol is low.

Together these two studies suggest that heavy prenatal alcohol use, above the UK recommended guidelines of one to two units once or twice a week, is a risk factor for prolonged damage to a child’s physical and mental development. However, one further study conducted in the US has reported findings suggesting that even a small amount of alcohol (equivalent to one UK unit) may be a risk-factor for behavioural problems for children at the age of six to seven.

The study recruited mothers who drank at least 0.5oz of absolute alcohol per day (equivalent to roughly one 148ml glass of 12% wine), those who drank less frequently, and women who did not drink at all. Children were assessed aged six-seven years via parental-reports of behavioural problems. Results indicated that children with any prenatal exposure to alcohol scored higher on behaviour scales related to aggression, delinquency, depression and anxiety and total problem score, regardless of the heaviness of use.

The addition of this study suggests that even a small amount of prenatal alcohol use may increase the risk for prolonged effects on a child’s mental health. A strength of these studies is that authors took into account the contribution of prenatal (maternal age, education and other drug use) and postnatal risk factors, (socioeconomic background, continued maternal alcohol and drug use and family structure) on the association between drinking and the child’s health, behaviour and learning.

However, there are some limitations in the interpretation of these findings. The studies used different measurements to capture prenatal alcohol use, eg units, ounces, US standard drinks, which can make comparison between study findings difficult. Similarly these studies cannot provide a definitive threshold for safe drinking during pregnancy. They can only indicate which levels of alcohol use in pregnancy confer the greatest risk.

Conclusions

The scientific literature doesn’t point towards a specific amount of alcohol that is safe to drink during pregnancy. However, research studies do suggest that drinking above the recommended one to two units, once or twice per week increases risk of harm to the foetus, newborn and child. This risk includes potential impairment of physical, behavioural, cognitive and learning ability.

These studies also indicate that heavy and binge drinking during pregnancy is associated with the greatest risk for long-term effects on the child. However, there is some evidence that even small amounts of alcohol may contribute to prolonged risk.

So, how much is too much? Recommendations of health governing bodies and research findings appear to signal that abstinence is probably the safest option when it comes to drinking while pregnant.

Dr Sally Adams is a lecturer in health psychology at the University of Bath. Her research examines the cognitive and behavioural mechanisms underlying alcohol and tobacco use. Find her on Twitter @SallyScientist