Consuming even low amounts of alcohol in pregnancy may be linked with higher chances of having a small baby and delivering prematurely, according to UK researchers.
They said women could use this new information to “inform their choices”, acknowledging that their research review was based on a handful of available studies and the effects they found were small.
“We wanted to give women the most up-to-date and reliable evidence in order to empower them”
The research team from Bristol University reviewed all the high quality scientific studies they could find on the effects of drinking small amounts of alcohol during pregnancy.
Small amounts were defined as one to two UK units, once or twice a week – the recommended maximum level given in the Department of Health’s previous guidance.
Two units of alcohol being equivalent to one pint of strong beer or a medium size glass (175ml) of light white wine.
The researchers looked at the effects on a wide range of health outcomes such as miscarriage, still birth, size at birth, and long term developmental delays, behavioural and cognitive deficits.
The review, published in the journal BMJ Open, found only seven studies with data on whether consuming small amounts of alcohol in pregnancy affected the size of babies at birth.
“This must be about women making a choice and what is important is that it is based upon the best available evidence”
The researchers found evidence that women who reported drinking even this small amount of alcohol were 8% more likely to deliver a small baby, with estimates ranging from a 2% to 14% rise.
The evidence that light drinking affected delivering prematurely was weaker and there was insufficient evidence on other health outcomes, noted the study authors.
Their evidence supports the new guidelines released by the Department of Health in 2016, which advise women not to drink any alcohol when pregnant or trying to conceive.
This guidance was based on a “better safe than sorry” principle, in the absence of strong evidence for or against actual harmful effects of alcohol to the unborn baby.
Drinking large amounts of alcohol is clearly linked to foetal alcohol syndrome (FAS) and increases the risk of miscarriage, premature birth and the baby having a low birth weight.
Review suggests alcohol best avoided during pregnancy
But the Bristol team emphasised that their review, which was funded by the National Institute for Health Research, referred to light drinking and that the effects they found were small.
In addition, they said that overall there was still some uncertainty, for example, on how light drinking in pregnancy affected other aspects of the baby’s health.
They highlighted that another reason to be cautious was that the association might not reflect a direct causal link.
Dr Luisa Zuccolo, who co-led the study, said: “Formulating advice on the basis of the current evidence is challenging, because we are still building the full picture of what happens to the unborn baby when small amounts of alcohol reach the bloodstream or brain.
“We wanted to give women the most up-to-date and reliable evidence in order to empower them to make an informed decision about drinking during pregnancy and balancing any possible risk with other factors in their lives,” she added.
Carmel Lloyd, head of education at the Royal College of Midwives, said: “We support the view of the research authors and our advice also remains that if you are pregnant or thinking of becoming pregnant then it is better to remove any doubt about the impact of alcohol and not drink it.
“However, this must be about women making a choice and what is important is that they make that choice based upon the best available evidence,” she said.
She added: “If pregnant women have concerns about their level of alcohol consumption in pregnancy, we encourage them to speak to their midwife who will be able to offer them advice and support.”
Dr Daghni Rajasingam, spokesperson for the Royal College of Obstetricians and Gynaecologists, said: “As there is no proven safe amount of alcohol women can drink during pregnancy, abstinence is the safest option, particularly for women trying to conceive or those in the first three months of pregnancy.
“While this study adds to the evidence that drinking one to two units of alcohol a week after the first 12 weeks of pregnancy is unlikely to have a harmful impact on the baby or pregnancy, we cannot rule out the risks altogether,” she said.
“It’s important that women are informed about the risks associated with heavy drinking during pregnancy, including fetal alcohol spectrum disorders and an increased risk of miscarriage, but healthcare professionals should also be open and honest about the limitations of the science in relation to drinking one to two units a week during pregnancy, supporting them in coming to a decision for themselves,” she added.