Morbidity and drugs in pregnancy: the influence of illness and drugs on the aetiology of congenital malformations.

In a prospective study involving 9,000 pregnant women, no cause-and-effect relationships have been established between morbidity recorded or drugs taken during early pregnancy and subsequent congenital malformations. The relationships that have been identified are largely explained by the influence of a history of a previous abnormal outcome of pregnancy (including abortion) and, to a lesser extent, by the influence of maternal anxiety on the diagnosis of doubtful malformations. It is also very unlikely that any drug in common use in 1964 had even a minor influence on congenital malformations recognisable in the first six weeks of life.