The association between prenatal alcohol exposure, fetal growth and preterm birth: evidence from a systematic review and meta-analyses
- Centre for Population Health Research, Curtin Health Innovation Research Institute, Curtin University, Perth, Australia
- Correspondence to Colleen M O’Leary
Centre for Population Health Research, Curtin Health Innovation Research Institute, Curtin University, Kent St, Bentley WA 6102, Australia;
Implications for practice and research
■ Women should be informed that a relatively low level of alcohol increases the risk of impaired fetal growth and preterm birth.
■ Health professionals should advise pregnant women that since it is difficult to estimate how much alcohol they are consuming, avoiding alcohol is best for the baby.
■ Pregnant women who drink heavily should be provided with counselling, antenatal services, and appropriate interventions in a non-judgemental and supportive environment.
■ Research examining the association between the dose and pattern of maternal drinking and fetal outcomes is needed.
Controversy surrounds the issue of alcohol and pregnancy. Whether it is safe for pregnant women to consume low levels of alcohol is hotly debated.1 ,2 While it is well recognised that heavy prenatal alcohol exposure can harm the fetus, methodological issues such as sample size limitations and measurement error, limit our ability to conclusively determine if low to moderate levels of prenatal alcohol exposure are harmful.3 The lack of scientific certainty has resulted in a range of opinions about whether pregnant women should be counselled to abstain from alcohol or advised that low levels of maternal alcohol consumption present low risk to the fetus.1 ,2
Patra et al undertook a systematic review and meta-analysis of papers investigating the relationship between prenatal alcohol exposure and low birthweight (2500 gm), small for gestational age (SGA <10th percentile) and preterm birth (<37 weeks). Two researchers reviewed the abstracts independently to identify studies meeting the inclusion criteria; original studies, cohort or case-control studies and those reporting RR, ORs or HRs. A standardised protocol was used for data extraction with 36 studies meeting the inclusion criteria providing 177 300 pregnant mothers for the low birthweight, 280 443 for preterm, and 136 949 for SGA analyses.
This study found no increased risk of impaired fetal growth or preterm birth with low levels of prenatal alcohol exposure, equivalent to an average of one ‘standard’ drink (international variation from 10 to 13 g). However, the risk increased when the mother consumed an average of two or more ‘standard’ drinks per day, with a clear dose response evident. The risk of impaired fetal growth and preterm birth was evident for maternal alcohol consumption in each of the trimesters.
The finding of no increased risk of impaired fetal growth or preterm birth from low levels of maternal drinking supports previous research findings.3 ,4 A major strength of this study over previous reviews was the addition of a meta-analysis incorporating 24 studies providing large numbers of women drinking at different levels during pregnancy. The statistical techniques used by the authors enabled them to address the heterogeneity between studies such as different study designs, methodology and populations.
A limitation of the meta-analysis was that most of the studies meeting the inclusion criteria did not provide information on maternal drinking patterns so the effect of dose per occasion could not be examined. Averaging of maternal alcohol consumption limits our ability to examine the effect of low, moderate and occasional binge drinking4 and future research should address this issue. Meta-analyses of the research evidence for other outcomes would enhance our knowledge as the association between prenatal alcohol exposure and other fetal effects, such as neurodevelopmental outcomes, may demonstrate a different pattern from that demonstrated by Patra for fetal growth and preterm birth.
While the findings of the meta-analysis should reassure women who have consumed alcohol at low levels during pregnancy, the risk to fetal growth and preterm birth increased with an average of two ‘standard’ drinks per day. Women should be aware that estimating the quantity of alcohol in a beverage is difficult and that the term ‘standard’ drink, used by researchers to quantify prenatal alcohol exposure, does not necessarily equate to one serving of alcohol. For example, a serving of wine or full-strength beer is generally 1.5–2 ‘standard’ drinks and the alcoholic intake can be much larger depending on the type of beverage, its alcohol content and the size of the drinking container. The caveat is that it easy to drink more alcohol than you think, therefore abstinence from alcohol is safest for the baby.