Association of light-to-moderate alcohol drinking in pregnancy with preterm birth and birth weight: elucidating bias by pooling data from nine European cohorts

Abstract

Women who drink light-to-moderately during pregnancy have been observed to have lower risk of unfavourable pregnancy outcomes than abstainers. This has been suggested to be a result of bias. In a pooled sample, including 193 747 live-born singletons from nine European cohorts, we examined the associations between light-to-moderate drinking and preterm birth, birth weight, and small-for-gestational age in term born children (term SGA). To address potential sources of bias, we compared the associations from the total sample with a sub-sample restricted to first-time pregnant women who conceived within six months of trying, and examined whether the associations varied across calendar time. In the total sample, drinking up to around six drinks per week as compared to abstaining was associated with lower risk of preterm birth, whereas no significant associations were found for birth weight or term SGA. Drinking six or more drinks per week was associated with lower birth weight and higher risk of term SGA, but no increased risk of preterm birth. The analyses restricted to women without reproductive experience revealed similar results. Before 2000 approximately half of pregnant women drank alcohol. This decreased to 39% in 2000-2004, and 14% in 2005-2011. Before 2000, every additional drink was associated with reduced mean birth weight, whereas in 2005-2011, the mean birth weight increased with increasing intake. The period-specific associations between low-to-moderate drinking and birth weight, which also were observed for term SGA, are indicative of bias. It is impossible to distinguish if the bias is attributable to unmeasured confounding, which change over time or cohort heterogeneity.

Alcohol Intake in Early Pregnancy and Spontaneous Preterm Birth: A Cohort Study

“…A number of studies published after this meta‐analysis including 2 large cohorts found that any alcohol intake was associated with higher risk of preterm birth (Aliyu et al, ; Miyake et al, ; Nykjaer et al, ; Salihu et al, ). However, other recent studies found no association (Baron et al, ; Cooper et al, ; Dale et al, ; Lundsberg et al, ; McCarthy et al, ; Meyer‐Leu et al, ; Sbrana et al, ; Smith et al, ; Strandberg‐Larsen et al, ), and one study indicated lower risk among drinkers compared to nondrinkers (Pfinder et al, ), which is in accordance with previous studies suggesting an apparently beneficial effect of a low‐to‐moderate alcohol intake (Albertsen et al, ; Jaddoe et al, ; Kesmodel et al, ). It has been discussed whether these findings may be due to residual confounding (the healthy drinker effect) caused by the inability to adjust for lifestyle and socioeconomic factors (Bailey and Sokol, ; Henderson et al, ; Henderson et al, ; Patra et al, ; Pfinder et al, ).…”

“…Kesmodel and colleagues () also reported a higher risk of spontaneous preterm birth among women drinking ≥ 10 drinks per week in the first trimester compared to women drinking <1 drink per week (unadjusted RR 3.22, 95% CI 1.07 to 9.67). Previous studies have indicated a U‐shaped association between average weekly alcohol intake and both spontaneous preterm birth (Kesmodel et al, ; McCarthy et al, ) and any preterm birth (Albertsen et al, ; Jaddoe et al, ; Kesmodel et al, ; Strandberg‐Larsen et al, ) with the lowest risks seen at an intake of 1 to 6 drinks per week compared to an intake of less than 1 drink per week. It has been suggested that the apparently beneficial effect of small doses of alcohol may be due to confounding by the “healthy drinker effect.” This may appear if drinking in small amounts is associated with a healthier lifestyle, or if women with chronic diseases are more likely to abstain from alcohol than healthy women (Howards, ; Howards, ; Kesmodel, ; Strandberg‐Larsen et al, ; Strandberg‐Larsen et al, ).…”

Changes in Alcohol Intake During Pregnancy in Spain, 1980 to 2014

“…We also identified a positive association but only with sporadic consumption, which may suggest a reduction in consumption frequency. Evidence regarding educational level and consumption was also inconsistent (McDonald et al., , ; Skagerstróm et al., ; Strandberg‐Larsen et al., ), and we failed to detect statistically significant associations in our sample. Although it may be worth noting that sporadic consumption was more likely among pregnant women with higher educational levels, estimates only approached statistical significance.…”

“…The only Spanish study that examined the evolution of consumption among expectant mothers described a declining trend throughout the territory (Martínez‐Frías et al., ). Other European countries (Kesmodel et al., ; Strandberg‐Larsen et al., ), together with the United States (Cil, ) and Australia (Callinan and Ferris, ; Cameron et al., ), have also experienced similar rapid declines.…”

Are antenatal interventions effective in improving multiple health behaviours among pregnant women? A systematic review protocol.

“…Despite the risks associated with SNAP health behaviours and the guidelines advising pregnant women of recommended health behaviours, the prevalence of SNAP health behaviours in pregnancy is high. Internationally, studies have found that 10-30% of women smoke tobacco during pregnancy (20)(21)(22)(23)(24), 97-100% do not meet all pregnancy food group recommendations (25,26), 20-80% consume alcohol (27,28), and 53-75% do not meet the recommended 150 minutes of moderate physical activity each week (29)(30)(31). The clustering of SNAP health behaviours is well established in the general population (32,33) and among pregnant women speci cally (34)(35)(36)(37)(38).…”