To evaluate the reliability of retrospective studies in the search for environmental causes of malformations, the following study was made: A retrospective interview was performed with mothers of 203 dead or malformed children and a control group of the same size and the replies were compared with those obtained in a prospective study of the same mothers made in the 5th month of pregnancy. The comparison dealt with information on the occurrence of nonchronic diseases and the consumption of drugs during early pregnancy. The results indicated that only about 25% of the prospectively collected information was accurately elicited in the retrospective study. In addition, the results showed that 2/3 of the positive replies in the retrospective study could not be confirmed from the prospective interview or information collected from other sources.
