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Dr. Mamluk and colleagues’ recent systematic review and publication in BMJ Open (1) carries with it a provocative title and over the past week its conclusions have garnered substantial attention by news organizations such as CNN (2), Newsweek (3), and the New York Post (4). Although we agree completely with the authors’ assertion that there is a significant gap in the literature concerning low levels of maternal alcohol consumption during pregnancy, we have some substantial concerns regarding misleading statements in the paper and inconsistencies between the methodology that was stated versus that which was conducted.
First, in the introduction, the authors claim that “Internationally, clinical guidelines recommend that pregnant women should abstain from heavy or ‘binge’ drinking”. Although technically correct, it is misleading since the messaging reported in the authors’ cited reference actually shows that nearly every country advises abstaining from any alcohol consumption during pregnancy – not just heavy or binge drinking. Furthermore, the authors state that “…UK guidelines advised women to avoid drinking alcohol while trying to conceive, and in the first trimester, but at the same time indicated that consumption should be restricted to within ‘1 to 2 UK units, one or twice a week.” Their statement makes it seem as though the UK message is contradictory regarding maternal alcohol consumption during pregnancy – it is not. In the 2016 UK Chief Medical Officers’ Lo...
First, in the introduction, the authors claim that “Internationally, clinical guidelines recommend that pregnant women should abstain from heavy or ‘binge’ drinking”. Although technically correct, it is misleading since the messaging reported in the authors’ cited reference actually shows that nearly every country advises abstaining from any alcohol consumption during pregnancy – not just heavy or binge drinking. Furthermore, the authors state that “…UK guidelines advised women to avoid drinking alcohol while trying to conceive, and in the first trimester, but at the same time indicated that consumption should be restricted to within ‘1 to 2 UK units, one or twice a week.” Their statement makes it seem as though the UK message is contradictory regarding maternal alcohol consumption during pregnancy – it is not. In the 2016 UK Chief Medical Officers’ Low Risk Drinking Guidelines (5) it is stated that “If you are pregnant or think you could become pregnant, the safest approach is not to drink alcohol at all, to keep risks to your baby to a minimum.” In regards to women who wish to stay below 1-2 units per day during pregnancy, they state, “Women who wish to stay below these levels need to be careful to avoid underestimating their actual consumption. The safer option is not to drink alcohol at all during pregnancy.” We feel the Chief Medical Officers’ message is quite clear.
We are more concerned with seeming inconsistencies between the authors’ stated methodology and decisions made during the conduct of their systematic review. The methods section is well articulated and thorough and the authors [appropriately] state that eligible studies [for their review] must have had “prospective assessment of prenatal alcohol exposure (ie, before birth).” In fact, the entire case-control study design is ineligible for this reason, and the increased potential for recall bias, possibly differential based on the pregnancy outcome, that is associated with retrospective assessment of alcohol consumption. However, a single US study (6) that the authors admit accounts for >90% of participants included in the meta-analysis for SGA and preterm birth, and therefore drives the meta-analyses on these two outcomes, and is either the only or one of two studies for stillbirth, placental abruption, placenta previa, and pre-eclampsia, does not meet the authors’ own criteria. In fact, the dataset used in the study assesses maternal alcohol consumption based on what is documented on the birth certificate (6). Not only is this not prospective assessment of maternal alcohol consumption and prone to substantial bias, but birth certificates have been reported repeatedly to be one of the worst sources of such information, with extremely poor sensitivity and positive predictive value (7-10). Even the authors of that study acknowledge the 1.3% prevalence of maternal alcohol consumption during pregnancy grossly underestimates what was to be expected based on national data (10-16%). Clearly, this study fails to meet the criteria for this systematic review; regardless, the poor quality of maternal alcohol consumption data from this study would preclude its inclusion in a systematic review searching for reliable evidence to address an important public health question. Considering the overwhelming influence this study has on the meta-analysis conducted by Mamluk and colleagues, we feel this calls into question any conclusions drawn for preterm birth and SGA, and well as non-meta-analysis summaries for stillbirth, placental abruption, placenta previa, and pre-eclampsia.
We are also a bit confused as to the authors’ decisions regarding the inclusion/exclusion of data from one of only three studies on the association between low maternal consumption of alcohol during pregnancy and FASD malformations. This 1989 study by Ernhart et al (11) assessed varying levels of maternal alcohol consumption and the “tally” of both craniofacial and total birth defects. Mamluk and colleagues report in their systematic review the results from Tables 2 and 3 from Ernhart et al., which shows no statistically significant increased ‘tally’ of birth defects for low alcohol consumers (>0.0, ≤0.1 average ounces of alcohol per day) compared to abstainers. Alcohol exposure was assessed prospectively during pregnancy and met Mamluk’s criteria. However, Ernhart and colleagues acknowledge that this method may not reflect alcohol use during the period at, or shortly after, conception (ie, before a woman knows she is pregnant). Therefore, they used an additional method – ‘estimated embryonic average ounces of alcohol per day’ – to estimate exposure during a time window that is critical for alcohol-related dysmorphology (11). This technique, too, seemed to fit Mamluk’s systematic review criteria since it was based on responses elicited prior to delivery/birth. Futhermore, Tables 6 and 7 from Ernhart et al. reveal a statistically significantly (p=0.042) increased ‘tally’ of craniofacial anomalies for low alcohol consumers (>0.0, ≤0.1 average ounces of alcohol per day) compared to abstainers, and a borderline significant results for total anomalies (p=0.06). We are curious as to why one seemingly relevant approach was included in their review, but not another.
We appreciate the desire for Mamluk and colleagues to contribute to this very important evidence base. We also agree that in epidemiology and clinical practice, we often do a poor job of communicating absolute risk; therefore, we were pleased to read the UK Chief Medical Officers’, statement, “The risk of harm to the baby is likely to be low if you have drunk only small amounts of alcohol before you knew you were pregnant or during pregnancy” to prevent undue stress for women who drank small amounts prior to realizing they were pregnant or even during early pregnancy (5). Clearly, Mamluk’s systematic review should be a call to action for researchers to provide more reliable evidence to all stakeholders. However, in light of the clear evidence for adverse effects of higher levels of alcohol consumption, and the fact that we do not know of a safe amount of alcohol use during pregnancy, we feel hesitant to propose changes to nearly every country’s messaging in support of abstinence. We are particularly concerned by the New York Post’s title of “Light drinking during pregnancy does not harm baby: study” that covered the findings of this review.
1. Mamluk L, Edwards HB, Savovic J, et al. Low alcohol consumption and pregnancy and childhood outcomes: time to change guidelines indicating apparently 'safe' levels of alcohol during pregnancy? A systematic review and meta-analyses. BMJ Open. 2017;7(7):e015410.
2. Howard J. CNN: Is light drinking while pregnant OK? 2017; http://www.cnn.com/2017/09/11/health/drinking-alcohol-pregnant-study/ind.... Accessed September 12, 2017.
3. Dovey D. Newsweek: Can You Drink While Pregnant? Even Light Drinking Can Cause Problems 2017; http://www.newsweek.com/can-you-drink-while-pregnant-even-light-drinking.... Accessed September 13, 2017.
4. Whittfield T. New York Post: Light drinking during pregnancy does not harm baby: study. 2017; http://nypost.com/2017/09/11/light-drinking-during-pregnancy-does-not-ha.... Accessed September 12, 2017.
5. Health UDo. UK Chief Medical Officers’ Low Risk Drinking Guidelines. . 2016; https://www.gov.uk/government/uploads/system/uploads/attachment_data/fil.... Accessed September 15, 2017.
6. Salihu HM, Kornosky JL, Lynch O, Alio AP, August EM, Marty PJ. Impact of prenatal alcohol consumption on placenta-associated syndromes. Alcohol (Fayetteville, NY). 2011;45(1):73-79.
7. Northam S, Knapp TR. The reliability and validity of birth certificates. J Obstet Gynecol Neonatal Nurs. 2006;35(1):3-12.
8. Piper JM, Mitchel EF, Jr., Snowden M, Hall C, Adams M, Taylor P. Validation of 1989 Tennessee birth certificates using maternal and newborn hospital records. Am J Epidemiol. 1993;137(7):758-768.
9. Reichman NE, Hade EM. Validation of birth certificate data. A study of women in New Jersey's HealthStart program. Ann Epidemiol. 2001;11(3):186-193.
10. Zollinger TW, Przybylski MJ, Gamache RE. Reliability of Indiana birth certificate data compared to medical records. Ann Epidemiol. 2006;16(1):1-10.
11. Ernhart CB, Sokol RJ, Ager JW, Morrow-Tlucak M, Martier S. Alcohol-related birth defects: assessing the risk. Annals of the New York Academy of Sciences. 1989;562:159-172.
It is concerning to read on page 1 of the introduction that “Internationally, clinical guidelines recommend that pregnant women should abstain from heavy or ‘binge’ drinking'". The reference cites the liquor industry social aspects organisation [http://www.iard.org/] as their source, which we admit find rather unusual. What is more unfortunate is the authors then misrepresent the content found on the industry website. Rather than the guidelines recommending the avoidance of heavy drinking, all of the 54 countries’ guidelines for alcohol and pregnancy advise abstinence, and the only exception is Bulgaria which offers a low-risk level for pregnant women who do choose to consume. This appears contradictory to the statement made by the authors in their introduction.