Background: When examining the association between prenatal alcohol exposure and fetal effects, epidemiological studies have ignored the timing and intensity of the exposure. This study investigates the effect of using dose, pattern and timing of consumption (‘composite’ method) for examining the association between prenatal alcohol exposure and fetal effects.
Methods: The ‘composite’ method resulted in six categories of exposure (abstinent, low, moderate, binge <weekly, binge 1-2x/week and heavy). The odds of language delay and child behaviour problems were calculated for the ‘composite’ method and then compared with an analysis using averaged estimates of <1 and 1+ drinks per day and with stratification by quantity ignoring dose per occasion. Data used for the analyses are from a 10% random sample of non-Indigenous women delivering a live infant in Western Australia (1995-1996) were invited to participate in an 8-year longitudinal survey (78% response rate n=2,224; 85% were followed-up at two-years, 73% (five-years), 61% (eight-years)).
Results: The effect of moderate and binge levels of exposure was only evident with the ‘composite’ method; anxious/depressed problems following first trimester moderate exposure OR 2.05 (95% CI 1.09;3.87) and following late pregnancy moderate (aggressive behaviour OR 1.90 (0.90-3.98)) and binge (language delay OR 3.00 (0.90;9.93)) exposure. Results for heavy levels of exposure were similar with each method. The estimates for late pregnancy were imprecise due to small numbers.
Conclusion: The ‘composite’ method of classification more closely reflects real life drinking patterns and better discriminates maternal drinking than the other methods, particularly low, moderate and binge levels.