Increase of ectopic pregnancy in Finland--combination of time and cohort effects.

The marked increase of ectopic pregnancy in Finland was studied in 5-year age groups from 1968-1984. In the early 1970s, the overall increase was attributable to women under 30 years of age, and in the early 1980s to women aged 30 years or more. The increase in the incidence rate of ectopic pregnancy per 100,000 women has taken place somewhat successively since the late 1960s in women aged 20-24, 25-29, 30-34, and 35-39 years. The incidence of ectopic pregnancy per 100,000 women increased by every successive 5-year cohort born since the late 1930s up to the cohort born in 1954-1958; thereafter, the birth cohorts have experienced an equal or even lower risk of ectopic pregnancy. The findings suggest that the large "baby boom" cohort (born in 1945-1954), with its high risk of ectopic pregnancy, is mainly responsible for the overall increase in the number of ectopic pregnancies seen in the past decade. When these cohorts end their reproductive years, the marked increase in the number of ectopic pregnancies in Finland may decrease, but the incidence rates will probably stay stable.