The risks of occasional drinking compared with abstinence during pregnancy are not well established in the literature, according to the authors of a comprehensive systematic review and meta-analysis.
“Despite the distinction between light drinking and abstinence being the point of most tension and confusion for health professionals and pregnant women and contributing to inconsistent guidance and advice now and in the past, our extensive review shows that this specific question is not being researched thoroughly enough, if at all,” Loubaba Mamluk, PhD, from the School of Social and Community Medicine at the University of Bristol in the United Kingdom, and colleagues report today in BMJ Open.
To determine the effects of low-to-moderate levels of maternal alcohol consumption (32 grams or less per week) on pregnancy and longer-term offspring outcomes, the investigators examined observational studies published from 1950 through July 11, 2016, of pregnant women or women trying to conceive who prospectively assessed prenatal alcohol exposure.
The 32 g/week cut-off was selected because this was the amount considered, until recently, the upper limit of acceptable — though not recommended — based on UK guidelines. The guidelines have since been updated to recommend that women abstain from all alcohol when pregnant or while trying to conceive, the authors write. This recommendation, which is consistent with those in the Centers for Disease Control and Prevention’s The Dietary Guidelines for Americans 2015-2020, is a precautionary recommendation rather than an evidence-based one, they note.
Of 4680 abstracts identified, 24 prospective and two quasi-experimental studies met the inclusion criteria and were included in the analysis.
The pregnancy-related outcomes of interest included stillbirth, miscarriage; gestational length; preterm delivery; hypertensive disorders of pregnancy; gestational diabetes; small for gestational age (SGA); low amniotic fluid; placenta previa; placental abruption; assisted delivery; Apgar score at birth; admission to neonatal unit; and congenital malformations. The studies were also reviewed for outcomes indicative of fetal alcohol spectrum disorder (FASD), including childhood growth restriction, cranium size and head circumference, developmental delays, behavior problems, cognitive impairment and IQ, and facial malformations.
Of all of the outcomes considered, only SGA had significant, though modest, association with low-to-moderate alcohol consumption (odds ratio [OR], 1.08; 95% confidence interval [CI], 1.02 to 1.14). The authors note, however, that this “was almost entirely driven by a single US study contributing 95% of the participants to this meta-analysis.” Moreover, neither a summary meta-analysis of birth weight nor a summary effect of risk of birth weight < 2500 g showed significant association with low consumption vs no consumption.
For preterm delivery, “[t]he meta-analysis yielded a summary odds ratio of 1.10 (95% CI 0.95 to 1.28), but there was substantial statistical heterogeneity between studies (I2=60%) due to a large Danish study reporting a protective effect,” the authors write. “” Thus, the authors note that the “estimates for preterm birth were also compatible with no association.”
The two main findings of the review, the authors write, are the “surprisingly limited” number of prospective studies addressing the effects of low levels of alcohol consumption in pregnancy, and the paucity of evidence indicating a harmful or safe limit of light alcohol consumption.
“The question we have attempted to address is very important given the mixed advice that women are given with regards to whether they should abstain completely or be allowed light alcohol consumption in pregnancy,” the authors state.
Referring to the notable lack of research evidence to address this question, the authors call for additional studies, “including those using designs that improve causal inference,” to better estimate the actual risks associated with light alcohol consumption in pregnancy.
Researchers out of Australia recently conducted one such study, reported here by Medscape Medical News. The study showed an association between all levels of prenatal alcohol exposure and craniofacial shape differences resembling those observed in FASD. Using craniofacial phenotyping, the investigators identified FASD-like differences in the midface and nose areas in the children exposed to even the lowest levels of alcohol in utero.
The finding from the Australian study “adds to what we found, in that there may be a link to harmful effects of light prenatal alcohol consumption to the infant,” Dr Mamluk said in an interview with Medscape Medical News. That study also may inform the communications between healthcare providers and pregnant women on this topic, she said.
“It may be helpful to share this new information when advising pregnant women not to drink,” Dr Mamluk said.
Although formulating guidance based on the current evidence is a challenge, “what we know is that low-levels of alcohol consumption have some effect, rather than a clear indication or evidence that there is no effect, which is an important distinction,” she said. ”[The] evidence from our review and this new research support the precautionary principle guiding the abstinence recommendation.”
The authors have disclosed no relevant financial relationships.
BMJ Open. Published online September 11, 2017. Full text
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