Reports that 1 pregnant woman in 3 in UK binge drink...

"A third of British women risk doing severe harm to their unborn babies by binge drinking during pregnancy," the Mail Online reports. While a concerning statistic, the evidence behind the headline is perhaps not as clear-cut as the Mail would lead its readers to believe.

This story has been prompted by the publication of a study comparing just over 17,000 women's alcohol consumption before and during pregnancy in the UK, Ireland, Australia and New Zealand. It also looked at which groups of women were more likely to report drinking alcohol in pregnancy.

While the overall study population was large, an overlooked fact not made clear in the media was that the study only included data from 651 women from the UK. The study also collected this data over a relatively long time – between 2004 and 2011 – and drinking habits may have changed since then.

Out of these 651 women, a third reported binge drinking (defined as drinking six units or more in one sitting) in their first trimester. Reassuringly, in all countries surveyed, this figure dropped dramatically in the second trimester, to around just 1%.

This pattern could suggest that women may not have known they were pregnant at the time of binge drinking, and stopped once they found out. Whether pregnant or not, it is best to avoid binge drinking.

Current NICE recommendations are that women abstain from drinking alcohol in the first trimester of pregnancy, as it can increase the risk of miscarriage. It is also linked to premature birth, and drinking heavily through pregnancy can result in foetal alcohol syndrome.

If you are pregnant and having problems controlling your drinking, you should contact your GP for advice.

Where did the story come from?

The study was carried out by researchers from Cork University Maternity Hospital and other hospitals and research centres in Ireland, the UK, Australia and New Zealand. The studies in the individual countries were funded by different governmental and charity and research bodies. For example, in the UK, funding was provided by the National Health Service (NHS), Biotechnology and Biological Sciences Research Council, University of Manchester Proof, Guy's and St Thomas’ Charity, Tommy's charity and Cerebra UK.

The study was published in the peer-reviewed BMJ Open. This is an open-access journal, so the study is free to read online or download as a PDF.

The UK media focuses on the UK results, but none appear to report that these figures come from just 651 women, and data was collected over a long time period (2004-2011). This is probably too small a sample size to confidently extrapolate it to current drinking habits among all pregnant women in the UK, as most of the headline writers have done.

Only The Guardian points out that the reported level of binge drinking dropped to around 1 in 100 women in the second trimester.

While not assessed in the study, this could suggest that the vast majority of women stopped binge drinking once they realised they were pregnant, to prevent harm to their baby.

The researchers do call for better ways to assess alcohol intake in pregnant women, to get a more reliable estimate of how many women do drink in pregnancy. For example, they suggest the possibility of a biological test, which would not require a woman to self-report consumption.

What kind of research was this?

This was an analysis of data collected in both prospective and retrospective cohort studies. It aimed to identify how many women drank alcohol before and during pregnancy in multiple countries, and identify the characteristics of women who were more likely to drink in pregnancy.

This is a suitable approach to assessing this question. Prospective studies are more likely to be reliable, as they enrol people and then continue to assess their habits, as opposed to asking them about the (sometimes distant) past.

It is difficult to assess people’s alcohol consumption, as it relies on people being truthful and accurate about how much they drink. This may be even more difficult in pregnant women, as they may feel guilt or stigma associated with drinking alcohol in pregnancy, making them less likely to report it.

The researchers hoped that by looking at results collected in different ways from countries that are generally similar, they might get an idea of which methods of assessing alcohol consumption in pregnancy give the most consistent results.

In addition, estimates from different studies may be affected by different ways in which drinking was measured, meaning that estimates are not entirely comparable.

What did the research involve?

The researchers used data collected in three studies – two retrospective studies from Ireland and one international prospective study.

The Growing up in Ireland (GUI) study was a national survey of a sample of mothers of 10,953 infants aged six to nine months, carried out in 2008 and 2009. Interviews were carried out face-to-face by a trained researcher. They were asked if they drank during pregnancy and, if so, how much on average they drank per week (pints of beer or cider, glasses of wine, measures of spirits or alcopops) in each trimester.

The Pregnancy Risk Assessment Monitoring System Ireland (PRAMS Ireland) study surveyed a sample of 718 women who had given birth to a live baby and been discharged from Cork University Maternity Hospital in 2012. These women completed three postal surveys between two and nine months after the birth of their baby. The surveys included questions about whether they drank alcohol, how much (glasses or bottles) of different types of alcohol they drank and how often (occasions per week or month) in the three months before pregnancy, and in each trimester.

The international Screening for Pregnancy Endpoints (SCOPE) study included 8,531 healthy women who had their first baby from 2004 to 2011 in Ireland, the UK, Australia and New Zealand. The study did not include women who had multiple pregnancies (e.g. twins), or had various medical complications, such as being at high risk of pre-eclampsia, or who had a baby that was small for its gestational age or born pre-term. Research midwives interviewed the participants at 15 and 20 weeks into their pregnancy. They asked the women if they drank alcohol before pregnancy or earlier than 15 weeks, or were still drinking alcohol at the time of the interview. If they reported drinking at any of these points, they were asked how many units or "binges" per week they were drinking up to the time of interview. If they reported stopping drinking alcohol during the study, they were asked when they stopped.

The researchers compared results from the different studies. They defined one unit of alcohol as 8-10g of pure alcohol, which was equivalent to one glass of wine (about 100-125ml), one small glass of sherry, a single "nip" of spirits, or half a pint of regular-strength lager. A can or small bottle/glass of regular-strength beer (300-330ml, 4-5% alcohol) was equivalent to 1.5 units of alcohol, and a bottle of alcopop was equivalent to 2 units of alcohol. Alcohol intake was classified as occasional (1-2 units/week), low (3-7 units/week), moderate (8-14 units/week) or heavy (greater than 14 units/week). Binge drinking was considered to be consuming six or more units per occasion.

The studies also collected other information from the women, and the researchers looked at what characteristics were more common among women who reported drinking alcohol during pregnancy.

What were the basic results?

There was variation in the amount of alcohol the women reported consuming across the different countries and across groups of women with different characteristics.

When looking at Ireland, women in the SCOPE study reported the highest levels of drinking:

90% of Irish women in the SCOPE study reported drinking before pregnancy, compared to 77% in PRAMS Ireland.
82% of Irish women in the SCOPE study reported drinking during pregnancy, compared to 46% in PRAMS Ireland and 20% in GUI.
59% of Irish SCOPE participants reported binge drinking before pregnancy, and 45% during pregnancy.
By the second trimester, the proportion of Irish women reporting drinking alcohol in SCOPE had dropped to 29%, similar to the level in the PRAMS study (31%), and women were drinking less.
The proportion of Irish women drinking remained similar across the trimesters in the PRAMS (about 30%) and GUI studies (about 10-15%).

When looking across different countries within the SCOPE study:

Women in Ireland were most likely to report drinking pre-pregnancy (90%) or binge drinking pre-pregnancy (59%), and those in Australia least likely (drinking 53%, bingeing 11%).
Women in Ireland were also most likely to report drinking at some point during pregnancy (82%) or binge drinking at some point during pregnancy (45%).
75% of women from the UK reported drinking at some point in pregnancy and 33% reported binge drinking at some point in pregnancy.
Binge drinking was much less common in the second trimester (average 0.4% of women) than the first trimester (average 23%) across all countries.

When looking at the characteristics of those who drank:

Non-Caucasian women in all studies were less likely to drink alcohol during pregnancy than Caucasian women.
Women who smoked were more likely to drink alcohol during pregnancy in all three studies.

How did the researchers interpret the results?

The researchers concluded that: "alcohol use during pregnancy is prevalent and socially pervasive in the UK, Ireland, New Zealand and Australia". They suggest that this shows low adherence to guidelines recommending complete abstinence or only low consumption, and that new policies and interventions are needed to reduce women’s alcohol consumption both before and during pregnancy. They also note that research is needed to identify more reliable ways to assess alcohol consumption in pregnancy, so they can more accurately tell how many women do drink during pregnancy.

Conclusion

This study provides information on reported alcohol consumption among pregnant women in four different countries. The study’s strengths are the relatively large number of women assessed overall (over 17,000) and that at least some of the data was collected prospectively.

The studies collected data on alcohol consumption in different ways – for example, in face-to-face interviews or by post – and interviews were carried out by either midwives or researchers. They also used different questions about alcohol consumption. This may mean that results are not directly comparable across the studies. The researchers were interested in whether, despite these different methods, there would be similar results across the studies. For example, the fact that women who smoked were more likely to report drinking alcohol in pregnancy across the studies suggests that this is more likely to be a reliable finding.

The researchers note that:

Their study included women who may be less disadvantaged than the general population, so results may not be as representative of more disadvantaged populations.
They only included women whose baby was born alive. This excludes women who had a miscarriage, and therefore may exclude the heaviest drinkers, as heavy or chronic alcohol use in early pregnancy has been linked to increased miscarriage risk.

Cultural differences and possible differences in guidance about alcohol consumption in pregnancy across the different countries may have influenced the results. The studies collected data across a wide time period, particularly the SCOPE study, which collected data from 2004 to 2011. Alcohol consumption may also have varied over this period.

Although the study was large overall, the number of women from some countries was small. For example, only 651 women from the UK were included, and 1,159 from Australia. Therefore, results may not be representative of the whole pregnant population in these countries.

The overall pattern of results is somewhat skewed, due to larger amount of data relating to women from Ireland and New Zealand.

Current UK NICE guidance recommends that women planning a pregnancy and pregnant women avoid drinking alcohol in the first three months (trimester) of pregnancy because it may increase risk of miscarriage.

If women choose to drink during pregnancy, they should drink no more than 1 to 2 UK units once or twice a week. NICE notes that there is still uncertainty regarding a safe level of alcohol consumption in pregnancy, but there is no evidence that this low level causes harm to the unborn baby.

Pregnant women should avoid getting drunk or binge drinking (drinking 5 standard drinks or 7.5 UK units on a single occasion), as this may harm the unborn baby.