Epidemiology of ectopic pregnancy during a 28 year period and the role of pelvic inflammatory disease.

OBJECTIVES: We analysed the epidemiology of ectopic pregnancy (EP) during a 28 year period, 1970-97, using methods applicable to ecological studies in order to test the hypothesis that a reduction of pelvic inflammatory disease (PID) will be associated with a decrease of EP.
METHODS: Hospital records of patients aged 15-54 admitted to our department of gynaecology were reviewed for EP and PID for the period 1 January 1970 to 31 December 1997. EP for the period 1970-4 was based on available statistics. The total number for EP was 1270 and for PID 2559. The total population for the catchment area was 100,000-120,000 during the study period. Incidences were age standardised and calculated using official population statistics to represent the average female population in the five 5 year periods 1970-4, 1975-9, 1980-4, 1985-9, 1990-4, and in each of the consecutive years 1995, 1996, and 1997. Incidences for EP were calculated per 1000 women and per 1000 pregnancies while those for PID per 1000 women. National statistical data of EP were available for 1975-94 and were used for comparison with the local study.
RESULTS: The EP incidences increased from 7.7 per 1000 pregnancies in the first 5 year period to 13.4 in the second, and continued to rise for another decade reaching the peak figures of 16.6 in 1985-9--that is, more than a twofold increase. Since then and to 1997 the EP incidence has decreased by 30%. PID admissions increased during the study period from 2.7 per 1000 women in the first 5 year period to 3.2 in the second. From then on they continuously decreased and reached a low of 0.5 in 1997. The greatest changes occurred in women < or = 24 years of age. The peak incidence for this age group was 7.7 in 1975-9, and the lowest was 0.4 per 1000 women in 1996. The greatest reduction of EPs was noted for women < or = 24 years old, from a high of 10.0 in 1975-9, coinciding with the peak incidence of PID, to a low of 4.0 in 1997, a reduction of 58.4%. The incidence of EP was two to three times higher in women > or = 25 years old, most obvious in those > or = 30 years, with peak figures of 20.9 per 1000 pregnancies in 1985-9, and 13.9 in 1997, a reduction of 33.4% and the lowest figures for the past 23 years. For women aged 25-29 years the incidence peaked in the previous 5 year period 1980-4--that is, one 5 year period later than for those < or = 24 years, which we interpret as cohort effects in relation to PID.
CONCLUSIONS: Reduction of PID was strongly associated with a decline of EP. The decline was greater and immediate for women < or = 24 years old, than for those > or = 25 years. The two to three times higher EP incidence in women > or = 25 years of age was most probably due to a cohort effect as the peak of PID occurred a decade earlier in women < or = 24 years old. Prevention of PID may not only reduce EP but also reduce adverse effects on tubal patency.