Screening for chlamydial infections and the risk of ectopic pregnancy in a county in Sweden: ecological analysis

BMJ 1998;316:1776-1780 ( 13 June )

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Screening for chlamydial infections and the risk of ectopic pregnancy in a county in Sweden: ecological analysis

Matthias Egger, reader in social medicine and epidemiology, ^a Nicola Low, lecturer in genitourinary medicine, ^b George Davey Smith, professor of clinical epidemiology, ^a Bo Lindblom, professor of obstetrics and gynaecology, ^c Björn Herrmann, consultant microbiologist. ^d

^a Department of Social Medicine, University of Bristol, Bristol BS8 2PR, ^b Department of Genitourinary Medicine, King's College School of Medicine and Dentistry, London SE5 9RS, ^c Department of Obstetrics and Gynaecology, University Hospital, S-751 85 Uppsala, Sweden, ^d Department of Infectious Diseases and Clinical Microbiology, University Hospital

Correspondence to: Dr Egger m.egger{at}bristol.ac.uk

Objectives: To analyse trends in rates of genital chlamydial infection and ectopic pregnancy between 1985 and 1995in a county in Sweden.
Setting: Uppsala county where screening for chlamydial infection, treatment, and contact tracing has been widespreadand where ectopic pregnancies are recorded.
Methods: Rates of chlamydial infections and ectopic pregnancy between 1985 and 1995 were calculated for women aged20-39 years. Poisson and linear regression were used to examinethe association between the risk of ectopic pregnancy and thecurrent rates of chlamydial infection and rates of chlamydialinfection from up to 5 years earlier.
Main outcome measures: Rates of chlamydial infection per 100 examinations, rates of ectopic pregnancy per 1000 pregnancies, rate ratios and 95% confidence intervals for an increase in chlamydial infections of 5 new cases per 100 examinations.
Results: 103 870 cervical samples from women aged 15-39 years were analysed; 5648 (5.4%) were positive for chlamydia. 51 630 pregnancies were analysed; 930 (1.8%) were ectopic. Bothrates declined over time. For women aged 20-24 years there wasa strong correlation between the rate of ectopic pregnancy andthe rate of chlamydial infection in the same year (r=0.93, P<0.001);among older women correlations were stronger with rates of chlamydialinfection occurring 1 or 2 years earlier. In Poisson regressionectopic pregnancy was most strongly associated with the currentrate of chlamydial infection among women aged 20-24 (rate ratio 1.85, 95% confidence interval 1.44 to 2.38), with the rate of infection 1 year earlier among 25-29 year olds (rate ratio 1.72,1.33 to 2.22) and 30-34 year olds (rate ratio 2.27, 1.53 to 3.37);and with the rate 2 years earlier among 35 to 39 year olds (rateratio 2.58, 1.45 to 4.60).
Conclusions: Declining rates of genital chlamydial infections have probably led to a fall in the rate of ectopic pregnancies.The timing of the decline in the rate of ectopic pregnancies varieswith age. Among young women falling rates of chlamydial infectionhave been accompanied by an immediate reduction in the rate ofectopic pregnancy.

Key messages

The effect of measures to diagnose and treat genital chlamydial infections on the risk of ectopic pregnancy was examined in a county in Sweden
Rates of chlamydial infection and ectopic pregnancy both declined between 1985 and 1995
Chlamydial infections seem to be the main cause of ectopic pregnancy in young women; the risk of ectopic pregnancy decreased concurrently with the decline in chlamydial infections
In older women the associations were less pronounced

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