Drinks containing alcohol were measured in standard, American ethanol units equaling 0.5 ounces of absolute alcohol: 340 ml can/bottle of beer (5% ethanol), 120 ml of wine (11% ethanol), 95 ml of wine (13.5% ethanol), or 44 ml of distilled spirits (43% ethanol). Respondents viewed pictures of standard containers of local brands to calibrate exact amounts consumed (Kaskutas and Graves, 2000, 2001; Kaskutas and Kerr, 2008). Questions on current drinking establish the method and calibration of reporting, and refresh recall before the timeline follow-back questions (Sobell et al., 1988, 2001) about the index pregnancy. Retrospective, post-natal reports of gestational alcohol use have proven to be accurate (Alvik, 2006a; Czarnecki et al., 1990; Hannigan et al., 2010).
