Women who have had chlamydia are at greater risk of an ectopic pregnancy because of a lasting effect of the infection.
A new study provides evidence for the first time of how chlamydia can increase the risk of an ectopic pregnancy .
In an ectopic pregnancy the embryo implants outside the womb, generally in the Fallopian tube.
Role of protein
University researchers found that women who had had the sexually transmitted infection were more likely to produce a particular protein in their Fallopian tubes.
Increased production of this protein - known as PROKR2 - makes a pregnancy more likely to implant in the Fallopian tube.
The study, funded by the Wellbeing of Women and the Medical Research Council, is published in the Americal Journal of Pathology.
It follows on from University research, which showed that production of a similar protein increased the likelihood of smokers having an ectopic pregnancy.
Chlamydia is the most common sexually transmitted infection in the UK.
It can be treated but often goes undiagnosed because it can occur without symptoms.
The infection is known to cause infertility as it can lead to scarring and blockages in the Fallopian tube.
This research shows, however, that chlamydial infection linked to ectopic pregnancy causes much more subtle changes in the Fallopian tube, without evidence of severe scarring.
The University of Edinburgh