Maternal drug histories and congenital malformations: limb reduction defects and oral clefts.

In a case control study, prescription data were examined for the three months before the last menstrual period and for the first trimester of pregnancy in (a) 115 mothers of children with limb reduction defects, (b) 676 mothers of children with oral cleft, and (c) an equal number of control mothers of normal babies from the same doctor's practice for each case. In the limb reduction study, the study mothers were prescribed more drugs generally although this did not reach statistical significance, nor were there significant differences between study and control mothers for individual groups of drugs. In the oral cleft study, significantly more drugs were prescribed to study mothers in the three months before the last menstrual period, and a similar trend, which did not reach statistical significance, was observed in the first trimester. Anticonvulsant drugs were prescribed significantly more frequently to study mothers during the whole period of the study. A significant association was also demonstrated between oral contraceptives taken in the three months before the last menstrual period and oral cleft, but doubt must remain concerning this relationship; the risk is not well understood and is likely to be nonspecific. A number of other significant associations were identified, although their importance in practice is uncertain in view of the confounding factors that may affect a study of this kind.