Characteristics influencing informed consent on a congenital malformations registry.

Maryland law requires that all babies born with "sentinel birth defects" be reported to the State Department of Health, but mothers may deny consent for further contact. Consent was not strongly related to maternal age, race, or self-reported data on exposures, smoking, and drugs but was much less likely if the infant was dead. Selection bias in congenital malformations research may lead to underrepresentation of lethal defects, but self-reported data appear to be unbiased.