The influence of secular effects and gravidity on the rate of ectopic pregnancy in a Norwegian population.

In order to assess the influence of secular effects and gravidity on the incidence rate of ectopic pregnancy, information from reproductive history questionnaires was obtained for 7804 gravid females identified through the Norwegian Twin Panel. The overall ectopic pregnancy incidence rate was 5.6 per 1000 estimated conceptions, with rates increasing for women born after 1950. Women experiencing their first pregnancy were at lowest risk for that pregnancy being ectopic. When women were stratified by whether they were born before or after 1950, gravidity still had an effect on the incidence rate of ectopic pregnancy. Conversely, year of birth was influential when stratifying by gravidity. The results obtained here suggest that the recent increase in the incidence of ectopic pregnancy is unrelated to the number of prior pregnancies.