Of all the risk factors for ectopic pregnancy ,which one is the commonest?

Risk factors for ectopic pregnancy are- * Surgery done for a prior tubal ectopic, feility restoration or sterilisation confer highest risk. After one previous ectopic pregnancy , the chance of another approximate 10 % . * Abnormal fallopian tube anatomy underlies may cause of total ectopic pregnancy. * Surgeries for a prior tubal pregnancy , for feility resolution confer the highest risk of tubal implantation. * Prior STD which can diso normal tubal anatomy is another common risk factor * One episode of salpingitis can be followed by subsequent ectopic pregnancy upto 9%. * Salpingitis isthmic nodosa , which is condition in which epithelium lined diveicula extend into hyperophied muscularis layer. * Congential fallopian tube anomalies, especially those secondary to in utero diethylstilbestrol exposure, can predispose. * Infeility, as well as the use of A to overcome it, is linked to substantively increased risk for ectopic pregnancy * However, with some contraceptive method failures ,the relative number of ectopic pregnancies is increased.