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Low-level drinking in early pregnancy 'harms baby'
The reported frequency and type of alcohol drunk was used to calculate the units consumed per week.
Based on their responses, women were categorised as non-drinking, drinking two or fewer units per week, or drinking more than two units per week.
Birth outcomes were obtained from hospital maternal records. The primary outcome was birth weight, but the researchers also looked at birth centiles (birth size compared with other babies, adjusted for maternal height, weight, ethnicity, how many children she had, and the birth weight and gender of the baby), premature birth (before 37 weeks of gestation) and babies being small for gestational age (below the 10th growth centile).
The researchers then looked at the association between drinking status and birth outcomes. They adjusted for confounders that included the mother's salivary cotinine (a biomarker of smoking status), pre-pregnancy weight, height, age, ethnicity, how many children she had, caffeine intake, and education.
What were the basic results?
Approximately three-quarters of women before pregnancy and more than half in the first trimester reported alcohol intakes of more than two units per week.
Just over a quarter of women reported drinking more than two units per week in the second or third trimester.
Alcohol consumption four weeks before pregnancy
Drinking more than two units per week four weeks before pregnancy was associated with lower birth weight (105.7g lower) and a 7.7 decrease in birth centile compared with not drinking. Drinking less than two units was not associated with lower birth weight or birth centile compared with not drinking.
Alcohol consumption during the first trimester of pregnancy
Drinking more than two units per week during the first trimester of pregnancy was associated with an approximate 100g reduction in birth weight and an 8.2 decrease in birth centile compared with not drinking.
Drinking more than two units per week was associated with increased odds of having a baby small for its gestational age (odds ratio (OR) 2.0, 95% confidence interval (CI) 1.2 to 3.4) and a premature birth (OR 3.5, 95% CI 1.1 to 11.2).
Drinking two units or less per week during the first trimester of pregnancy was associated with an approximate 100g reduction in birth weight and a 5.8 decrease in birth centile compared with not drinking. Drinking two units or less per week was also associated with increased odds of having a preterm birth (OR 4.6, 95% CI 1.4 to 14.7).
Alcohol consumption during the second and third trimesters of pregnancy
Drinking more than two units per week during the second trimester of pregnancy was associated with an approximate 100g reduction in birth weight, and during the third trimester of pregnancy was associated with an approximate 50g reduction in birth weight compared with not drinking.
How did the researchers interpret the results?
The researchers concluded that, "Maternal alcohol intake during the first trimester was found to have the strongest association with foetal growth and gestational age. Women who adhered to guidelines in this period were still at increased risk of adverse birth outcomes even after adjustment for known risk factors.
"Maternal alcohol intakes which exceeded the recommendations in the period leading up to pregnancy were also found to be associated with foetal growth, suggesting that the [period around conception] could be particularly sensitive to the effects of alcohol on the foetus.
"Our results highlight the need for endorsing the abstinence-only message, and further illuminate how timing of exposure is important in the association of alcohol with birth outcomes, with the first trimester being the most vulnerable period."
This cohort study suggests that women who are planning to conceive and who are pregnant should abstain from alcohol. Drinking more than two units of alcohol per week was associated with adverse birth outcomes in all trimesters.
In addition, the study found that women who reported limiting drinking to less than two units per week during the first trimester of pregnancy were also at increased risk of adverse birth outcomes.
This study has the strength that it associated alcohol intake at three time points, covering different periods of pregnancy. Alcohol intake was assessed during pregnancy and not after birth, reducing the possibility of recall bias. In addition, it adjusted for a number of confounders and used an objective measure of smoking.
However, the study was originally designed to assess the impact of caffeine intake on birth outcomes. Alcohol intake was self-reported, and there is the possibility of under-reporting. Few women had data on alcohol consumption in the third trimester (30% of the original cohort).
Also, despite the fact that the researchers adjusted for a number of confounders, it is possible there are other factors that explain the association seen.
This research provides further evidence for not drinking during pregnancy. However, for now it is unclear whether consideration of this study alongside other evidence will lead to a change in NICE or Department of Health recommendations around alcohol use during pregnancy.
In the UK, the Department of Health currently recommends that pregnant women and women trying to conceive should avoid alcohol altogether, and, if they choose to drink, should never drink more than one to two units once or twice a week, and never get drunk.
The most recent NICE guidance on Antenatal Care (2008) specifically advises that women trying to conceive, and those in the first three months of pregnancy, should avoid drinking alcohol, as this may be associated with an increased risk of miscarriage.
After this, if women choose to drink during pregnancy they should drink no more than one to two units once or twice a week. NICE says that, "Although there is uncertainty regarding a safe level of alcohol consumption in pregnancy, at this low level there is no evidence of harm to the unborn baby."
The organisation advises that getting drunk or binge drinking should be avoided throughout pregnancy, as this may be harmful to the unborn baby.
"Drinking alcohol early in pregnancy, even in small amounts, increases chances of harming your baby," reports The Independent, one of several news outlets to report on the latest study on the risks of drinking during pregnancy...
Links to Headlines
Light drinking 'is preterm risk'. BBC News, March 11 2014
Middle-class mothers' alcohol risk to babies. The Daily Telegraph, March 10 2014
Drinking alcohol early in pregnancy, even in small amounts, increases chances of harming your baby, study finds. The Independent, March 10 2014
Links to Science
Nykjaer C, Alwan NA, Greenwood DC. Maternal alcohol intake prior to and during pregnancy and risk of adverse birth outcomes: evidence from a British cohort. Journal of Epidemiology and Community Health. Published March 10 2014
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