These factors include any previous pelvic or abdominal surgery, and pelvic infection. Chlamydia trachomatis has been linked to 30-50% of all ectopic pregnancies. The exact mechanism of this association is not known but it has been proposed that in addition to distortion of tubal architecture, it may to be due to an effect on the tubal microenvironment. Ectopic pregnancy is more common in women attending infertility clinics even in the absence of tubal disease. In addition, the use of ART increases the rate of ectopic pregnancies. In vitro fertilisation (IVF) is associated with an ectopic pregnancy risk of 2-5% and it may be higher than this where there is tubal disease.