Increased production of this protein, known as PROKR2, makes a pregnancy more likely to implant outside of the womb.
The study follows on from research, also at Edinburgh University, 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 research shows, however, that chlamydia causes “much more subtle changes” in the Fallopian tube, without evidence of severe scarring.
The study, published in the American Journal of Pathology, was funded by the Wellbeing of Women and the Medical Research Council.
Dr Andrew Horne, of Edinburgh University’s centre for reproductive biology, said: “We know that chlamydia is a major risk factor for ectopic pregnancy but until now we were unsure how the infection led to implantation of a pregnancy in the Fallopian tube.
“We hope that this new information allows health care providers to give women accurate information about risks following chlamydial infection and to support public health messages about the importance of safer sex and chlamydia testing.”
Director of The Ectopic Pregnancy Trust, Helen Wilkinson, said:
“We welcome any research that investigates the causes of ectopic pregnancy, a condition which causes both physical and emotional
trauma for many.
“Having data that explains how chlamydia can cause ectopic pregnancies provides us with greater understanding of the condition and gives us even more means to raise awareness of the importance of safe sex and sexual health testing for those who are sexually active.
“Any research that can help to reduce the incidence of ectopic pregnancy is extremely valuable”
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