Maternal alcohol drinking during pregnancy and offspring trajectories of height, weight and head circumference

In Denmark, United Kingdom, Australia and Ireland it has been estimated that between 37% and 81% of fetuses are exposed to alcohol in pregnancy (1-5). While the hazards of heavy alcohol consumption in pregnancy on birth outcomes including preterm birth and birth weight are well recognized, the effects of moderate-low levels of alcohol drinking in pregnancy are less clear both at birth and in particular longitudinally. The association between alcohol use during pregnancy and postnatal growth throughout childhood is not well established. Studies which focus on postnatal growth are a priority (6, 7) if consensus on safe alcohol recommendations for pregnant women is to be reached.

Aim : To investigate whether different patterns of alcohol use during pregnancy adversely affect height, weight and head circumference between birth and 10 years

Objective #1 Recent work conducted using the ALSPAC data investigated maternal smoking during pregnancy and offspring trajectories of height and adiposity up to age 10 (8). We propose to replicate the approach taken in this analysis in an investigation of the associations between different levels of alcohol consumption during pregnancy and height, weight and head circumference trajectories between birth and age 10 years.

Briefly, we will estimate the association between maternal drinking during pregnancy (any versus none and by dose) and trajectories of height, weight and head circumference that have previously been developed using multilevel models by Laura Howe and Andrew Smith. In keeping with Lewis and colleagues' recent categorisation of alcohol use in pregnancy (9) moderate alcohol consumption will be defined as equal to 1-6 drinks on average per week during pregnancy, heavy consumption will be defined as consumption of greater than 6 drinks per day and binge drinkers will be classified as women who report consuming more than 4 units of alcohol at 18 and 32 weeks of pregnancy. This classification will be examined with reference to the growth trajectories of women who abstained from alcohol during pregnancy.

Covariates adjusted for will include maternal age, ethnicity, maternal education, household occupational class, parity, maternal height, paternal height, maternal BMI, smoking during pregnancy, and other key variables. We will also consider drug use as a potential confounder, but this has a very low prevalence, so we will investigate whether or not it is possible/appropriate to include in analyses.

Objective #2 Residual confounding is often a significant limitation in studies of fetal alcohol exposure and infant outcomes. The relationship between alcohol use during pregnancy and growth outcomes at birth could be confounded by shared familial characteristics as has been suggested for the relationship between smoking during pregnancy and growth (8). For this part of the analysis, we will compare the associations of maternal alcohol consumption during pregnancy to the woman's partners in order to explore the presence of unmeasured confounders. This will allow us to estimate the extent to which any associations detected are likely to be the result of unmeasured genetic, socioeconomic or behavioural confounders.

Partner alcohol consumption was collected in a questionnaire sent to them at 18 weeks gestation. Partner alcohol consumption will be classified as moderate, heavy and/or binge in line with UK recommendations of no more than 21 units per week and no more than 4 units in one occasion. We will run the analysis specified in objective #1 both with mutual adjustment for partner alcohol consumption and for partner consumption alone adjusting for covariates already specified.

As a further tool for the assessment of potential unmeasured confounding, we will compare the growth trajectories of children whose mothers drink alcohol during pregnancy with those who do not drink during pregnancy but resume alcohol consumption shortly after delivery.

References

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2. Kelly Y, Sacker A, Gray R, Kelly J, Wolke D, Quigley MA. Light drinking in pregnancy, a risk for behavioural problems and cognitive deficits at 3 years of age? International Journal of Epidemiology. 2009;38(1):129-40.

3. Bakker R, Pluimgraaff LE, Steegers EAP, Raat H, Tiemeier H, Hofman A, et al. Associations of light and moderate maternal alcohol consumption with fetal growth characteristics in different periods of pregnancy: The Generation R Study. International Journal of Epidemiology. 2010;39(3):777-89.

4. Andersen AMN, Andersen PK, Olsen J, Gronbaek M, Strandberg-Larsen K. Moderate alcohol intake during pregnancy and risk of fetal death. International Journal of Epidemiology. 2012.

5. Mullally A, Cleary BJ, Barry J, Fahey TP, Murphy DJ. Prevalence, predictors and perinatal outcomes of peri-conceptional alcohol exposure - retrospective cohort study in an urban obstetric population in Ireland. BMC Pregnancy and Childbirth. 2011;11.

6. Patra J, Bakker R, Irving H, Jaddoe V, Malini S, Rehm J. 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. BJOG: An International Journal of Obstetrics & Gynaecology.

7. Henderson J, Gray R, Brocklehurst P. Systematic review of effects of low-moderate prenatal alcohol exposure on pregnancy outcome. BJOG: An International Journal of Obstetrics & Gynaecology. 2007;114(3):243-52.

8. Howe LD, Matijasevich A, Tilling K, Brion MJ, Leary SD, Smith GD, et al. Maternal smoking during pregnancy and offspring trajectories of height and adiposity: comparing maternal and paternal associations. International journal of epidemiology. 2012;41(3):722-32.

9. Lewis SJ, Zuccolo L, Smith GD, Macleod J, Rodriguez S, Draper ES, et al. Fetal Alcohol Exposure and IQ at Age 8: Evidence from a Population-Based Birth-Cohort Study. PloS one. 2012;7(11):e49407.