Recall bias in a case-control surveillance system on the use of medicine during pregnancy.

It is important to study possible teratogenic effects of drugs used during pregnancy. Many studies of this type rely upon case-control designs in which drug intake is recalled by the mothers after having given birth. Recall bias in this situation may lead to spurious associations. We looked for indicators of recall bias by comparing self-reported drug intake with medically notified intake for specific diseases in the Hungarian Case-Control Surveillance System of Congenital Abnormalities, which includes 22,865 cases with congenital abnormalities and 39,151 controls. Recall error was present, especially for drugs used for a short time period. Furthermore, the timing of drug intake was reported slightly closer to the time of interview for cases compared than for controls. Severe or visible congenital abnormalities did not appear to be more conducive to recall bias than other abnormalities under study. A case-control surveillance system of this type may frequently cause spurious associations, with biased odds ratios up to a factor of 1.9.