Dose-response relationship between alcohol consumption before and during pregnancy and the risks of low birthweight, preterm birth and small for gestational age (SGA)-a systematic review and meta-analyses

Abstract

Background: Descriptions of the effects of moderate alcohol consumption during pregnancy on adverse pregnancy outcomes have been inconsistent.

Objective: To review systematically and perform meta-analyses on the effect of maternal alcohol exposure on the risk of low birthweight, preterm birth and small for gestational age (SGA).

Search strategy: Using Medical Subject Headings, a literature search of MEDLINE, EMBASE, CINAHL, CABS, WHOlist, SIGLE, ETOH, and Web of Science between 1 January 1980 and 1 August 2009 was performed followed by manual searches.

Selection criteria: Case-control or cohort studies were assessed for quality (STROBE), 36 available studies were included.

Data collection and analysis: Two reviewers independently extracted the information on low birthweight, preterm birth and SGA using a standardised protocol. Meta-analyses on dose-response relationships were performed using linear as well as first-order and second-order fractional polynomial regressions to estimate best fitting curves to the data.

Main results: Compared with abstainers, the overall dose-response relationships for low birthweight and SGA showed no effect up to 10 g pure alcohol/day (an average of about 1 drink/day) and preterm birth showed no effect up to 18 g pure alcohol/day (an average of 1.5 drinks/day); thereafter, the relationship showed a monotonically increasing risk for increasing maternal alcohol consumption. Moderate consumption during pre-pregnancy was associated with reduced risks for all outcomes.

Conclusions: Dose-response relationship indicates that heavy alcohol consumption during pregnancy increases the risks of all three outcomes whereas light to moderate alcohol consumption shows no effect. Preventive measures during antenatal consultations should be initiated.

Figure 1

Results of systematic review of the relationship between maternal alcohol consumption and low birth weight, preterm birth and small-size-for-gestational age (SGA)

Figure 2. Relative risks for low birth weight comparing alcohol consumption versus no alcohol consumption (28 studies)

*The unadjusted pooled relative risk does not include unadjusted estimates from adjusted studies Unadjusted I² = 89%, 95% CI (84% – 93%), p<0.001 Adjusted I² = 62%, 95% CI (41% – 75%), p<0.001 Overall I² = 80%, 95% CI (73% – 85%), p<0.001

Figure 3. Relative risks for preterm birth comparing alcohol consumption versus no alcohol consumption (21 studies)

*The unadjusted pooled relative risk does not include unadjusted estimates from adjusted studies Unadjusted I² = 91%, 95% CI (86% – 94%); p <0.001 Adjusted I² = 64%, 95% CI (31% – 81%), p <0.001 Overall I² = 89%, 95% CI (84% – 92%), p <0.001

Figure 4. Relative risks for SGA comparing alcohol consumption versus no alcohol consumption (11 studies)

*The unadjusted pooled relative risk does not include unadjusted estimates from adjusted studies Unadjusted I² = 93%, 95% CI (83% – 97%); p <0.0001 Adjusted I² = 82%, 95% CI (65% – 91%), p <0.0001 Overall I² = 92%, 95% CI (88% – 95%), p <0.0001

Figure 5. Meta-analysis 19 studies* showing the dose-response relationship between maternal alcohol consumption and low birth weight

* For the information supporting this figure, please see the details in Supplementary Table S3

Figure 6. Meta-analysis of 14 studies* showing the dose-response relationship between maternal alcohol consumption and preterm birth

* For the information supporting this figure, please see the details in Supplementary Table S4

Figure 7. Meta-analysis of 8 studies* showing the dose-response relationship between maternal alcohol consumption and SGA

* For the information supporting this figure, please see the details in Supplementary Table S5