Alcohol Exposure in Pregnancy Has No Adverse Effect on Birth Weight
Despite the general consensus that excessive alcohol consumption should be avoided prior to and during pregnancy, there is very little data on the effects alcohol consumption in early gestation has on birth outcomes.
Review
McCarthy FP, et al. Association between maternal alcohol consumption in early pregnancy and pregnancy outcomes. Obstet Gynecol. 2013 Oct;122(4):830-7. http://www.ncbi.nlm.nih.gov/pubmed/24084541.
Using data from 5,628 nulliparous women from Ireland, England, Australia, and New Zealand recruited to the Screening for Pregnancy Endpoints (SCOPE) study, this prospective cohort study evaluated the association between alcohol exposure before and during pregnancy and adverse pregnancy outcomes.
Study Methods
Each patient underwent an initial exam and interview at 15 weeks gestation with a standardized questionnaire administered by a research midwife, through which the patient self-reported the frequency and amount of alcohol she consumed prior to and during the first 15 weeks of her pregnancy. Such alcohol consumption was classified as occasional (1-2 drinks/week), low (3-7 drinks/week), moderate (8-14 drinks/week), or heavy (>14 drinks/ week), with binge consumption defined as >6 drinks in one session.
Concerning adverse pregnancy outcomes, spontaneous preterm birth was defined as spontaneous labor with delivery at <37 weeks, small for gestational age (SGA) was defined as birth weight below the tenth percentile as adjusted for factors such as gestational age and ethnicity, and preeclampsia was defined by standard criteria of blood pressure, urine protein, and/or end-organ dysfunction at or after 20 weeks.
The initial analysis explored the relationship between the volume of alcohol consumed and the pregnancy outcome. To clarify the effect of chronic alcohol exposure, as opposed to periodic bursts of high exposure, those who reported binge drinking were excluded from the initial analysis.
A secondary analysis explored alternate classifications of alcohol consumption — including abstinent, quit before conception, quit before 15 weeks, and continued at 15 weeks — and pregnancy outcome, while a further analysis explored the relationship of binge drinking to pregnancy outcome.
Results and Outcomes
According to the authors, 40% of the participants reported no alcohol use in pregnancy, 19% reported occasional use, 25% reported low use, 11% reported moderate use, and 5% reported heavy use. Additionally, 34% reported binge drinking in the 3 months prior to conception, and 23% reported binge drinking in the first 15 weeks of pregnancy, of which 15% reported at least 2 episodes of binge alcohol consumption during that time period.
However, no correlation was found between the amount or timing of alcohol intake in the first 15 weeks of gestation and an increased risk for SGA or low birth weight. Consumption of alcohol during the first 15 weeks of pregnancy was also not associated with a change in the odds of spontaneous preterm birth, regardless of binge use. Finally, there was no significant difference in the odds of developing preeclampsia among those who consumed alcohol before and during pregnancy as compared to the control group.
Conclusion
Although alcohol consumption during pregnancy was common among the participants, no association was found between alcohol intake before 15 weeks of gestation and an SGA fetus, low birth weight infant, spontaneous preterm birth, or preeclampsia, regardless of the amount or timing of drinking.
Commentary
Despite the general consensus that excessive alcohol consumption should be avoided prior to and during pregnancy, there is very little data on the effects alcohol consumption in early gestation has on birth outcomes. This has led to different agencies publishing different recommendations,* even though the result of chronic and binge alcohol consumption in early pregnancy remains unknown.
The strengths of this study included its ability to parse out details on the timing and volume of alcohol consumption in an especially vulnerable trimester. Because the study was prospective, the authors were also better able to control for potential confounders.
However, the study’s design had several weaknesses. The timing of enrollment at 15 weeks of gestation meant that alcohol consumption implicated in the loss of an early pregnancy was not included in the final analysis. Indeed, 198 of the 8,531 women initially invited to participate in the study were excluded because they miscarried or had terminated their pregnancies before 15 weeks, and such loss of pregnancy in the first trimester may potentially be influenced by alcohol intake.
By focusing solely on pregnancy outcomes, this study excluded the long-term physical and neurocognitive effects of in utero alcohol exposure on children. Early pregnancy is a time when the fetus is particularly vulnerable to teratogens such as alcohol. Fetal alcohol spectrum disorders like fetal alcohol syndrome (FAS) — which results from the chronic use of alcohol (>1 oz/day) prior to and during pregnancy — is prevalent and involves a lifetime of consequences, which is a major reason why women are counseled to avoid alcohol while pregnant. Because this study did not address the long-term physical, neurological, and developmental effects on the fetus, its practical value is limited, and it must not be used to argue that alcohol consumption is acceptable during pregnancy.
Nevertheless, the study helps clarify the effects of alcohol consumption on the outcome of pregnancy with respect to birth weight, premature labor, preeclampsia, and SGA — relationships that were not clearly established in earlier research. For the many women who inadvertently drink alcohol in early gestation, not yet realizing they are pregnant, this study provides good evidence with which to counsel them on the likely outcomes of their pregnancies, as well as to help assuage any guilt that may arise from drinking during this time.
*The American Congress of Obstetricians and Gynecologists (ACOG) advises avoiding all alcohol before and during pregnancy, while the Royal College of Obstetricians and Gynaecologists (RCOG) and the UK Department of Health (DOH) suggests limiting consumption to 1-2 alcohol units 1-2 times/week. A recent systematic review and meta-analysis on the topic that was plagued by the shortcomings inherent to those types of studies found consumption of 1.25 drinks/day throughout pregnancy increased the risk of SGA, preterm birth, and delivery of a low birth weight infant in a dose-responsive manner, although less alcohol consumption was not associated with those outcomes.
Still, family physicians should encourage women to abstain from alcohol or, at a minimum, limit their consumption to <1 oz on an infrequent basis when they are trying to get pregnant, as well as throughout their pregnancies. For those who become pregnant following exposure to alcohol, this study offers guidance on understanding the risks.
About the Authors
Katherine Marino, MD, is a recent graduate of the University of Massachusetts Medical School (UMMS) in Worcester, MA.
She was assisted in writing this article by Frank J. Domino, MD, Professor and Pre-Doctoral Education Director for the Department of Family Medicine and Community Health at UMMS and Editor-in-Chief of the 5-Minute Clinical Consult series (Lippincott Williams & Wilkins).
