The authors investigated whether maternal or paternal periconceptional use of recreational drugs increased the nsk of having neural tube defect (NTD)-affected pregnancies using a population-based case-control study of fetuses and liveborn infants with NTDs among 1989-1991 California births. Face-to-face interviews were conducted with mothers of 538 (88% of eligible) NTD cases and 539 (88%) nonmatformed controls, usually within 5 months of delivery. Periconceptional maternal use of cocaine (odds

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... ratio (OR) = 0.74, 95% confidence interval (Cl) 0.40-1.4), amphetamines/speed (OR = 0.68, 95% Cl 0.39-1.2), or marijuana (OR = 0.64, 95% Cl 0.43-0.95) or preconceptional use of alcohol as <1 drink/day (OR = 0.80, 95% Cl 0.62-1.0) or ^1 dnnk/day (OR = 0.69, 95% Cl 0.42-1.2) or of cigarettes as <1 pack/day (OR = 0.90, 95% Cl 0.65-1.2) or &1 pack/day (OR = 0.59, 95% Cl 0.36-0.96) did not increase the risk for delivering NTD-affected offspring. Risks were not substantially altered after adjustment for maternal age, race/ethnicity, vitamin use, education, and household income. Increased NTD risk was also not generally associated with patema) drug use. The authors could not discern whether the decreased risks observed for these maternal exposures reflected a true association or were due to reporting bias, a disproportionate number of drug-exposed NTD cases among spontaneous abortuses that could not be ascertained, or some other bias.