New Zealand contraception and health study: design and preliminary report. New Zealand Contraception and Health Study Group.

The New Zealand contraception and health study is investigating the potential health risks associated with oral contraceptives, intrauterine contraceptive devices and injectable medroxy-progesterone acetate. This prospective observational study, begun as a pilot study in 1980, will record for at least six years the health of approximately 7500 women divided into three groups of equal size according to contraceptive method at entry. A major objective is to compare the incidence of dysplasia, carcinoma in situ and invasive carcinoma of the cervix in each group. This paper describes the design of the study and reports its progress.