Case-control studies on the effect of sex steroids on women and their offspring

Abstract

This paper discusses the case-control method for studies of birth defects and breast tumors as side effects of oral contraception (OC). The term case-control is used for any investigation which seeks to compare exposure frequencies between diseased and nondiseased groups. Case-control studies have 2 handicaps: 1) relative risk is expressed in terms of exposure among the diseased and 2) exposure is ascertained after the disease has occurred which can increase the possibility of obtaining biased exposure information. In order to eliminate the problem of bias each study must be designed to assure procedural excellence and absolute equality in the ascertainment of exposure in cases and controls. Careful evaluation of all sources of bias is an integral part of the case-control study procedure. Case-control studies are the strongest analytic epidemiological tools for the study of causal mechanisms of diseases; the most immediate problem investigators encounter is selection of the case and control population. The authors have applied their method of the case-control study to a study of 317 cases of breast cancer taken from the 1970-75 files at the New York State Cancer Registry. Age at diagnosis was classifed at less than 35 and at 35-44. To conduct this study the authors first conducted 2 separate case-control investigations to determine whether early pregnancy protects against breast cancer and whether the sex of the 1st child can be a risk of breast cancer in young women; they found that the male offspring has a uniformly greater effect of risk especially under 35 years of age. The same method was used in a case-control study of the association between OC and cardiac fetal malformations and results were compared to those of 2 similar studies that had been conducted with a different method. It was that the differences in relative risk between the 3 studies were likely to be due to methodological differences in the studies specifically the differences in case selection.