Alcohol consumption during pregnancy was measured in the following ways:Pattern of drinking reflecting episodic heavy drinking (primary exposure variable)—at both 18 and 32 weeks gestation, the mother was asked the number of days in the previous 4 weeks (i.e. reflecting 14–18 and 28–32 weeks gestation) on which she had consumed the equivalent of at least 4 units of alcohol. Examples were provided to confirm that one drink was equivalent to 1 unit (8 g) of alcohol. For analyses, this primary exposure variable reflected the consumption of ≥4 drinks in a day (binge-pattern drinking) on at least one occasion versus none.Frequency and quantity of drinking—at 18 weeks, the mother was asked the frequency and quantity of her drinking during the previous 2 weeks or around the time she first felt the baby move. Response categories provided were never, <1 glass per week, ≥1 glass per week, 1–2 glasses a day, 3–9 glasses a day or ≥10 glasses a day. At 32 weeks, she was asked the amount she usually drank in a day at that time. For analyses, daily drinking was defined as an average of at least one drink a day at either time point.
