Which of the following is a major risk factor for an ectopic pregnancy?

A major risk factor for ectopic pregnancy is a history of salpingitis, which refers to inflammation of the fallopian tubes. This condition can lead to scarring, adhesions, or blockage of the tubes, significantly increasing the likelihood of an embryo implanting outside of the uterine cavity. The damage caused by salpingitis can result from previous infections, particularly sexually transmitted infections, which may compromise the structural integrity of the fallopian tubes and impede the normal movement of the embryo toward the uterus.

Other factors that could influence the risk of ectopic pregnancy include previous surgery on the fallopian tubes, certain infertility treatments, or pelvic inflammatory disease. However, among the options provided, a history of salpingitis stands out as a definitive risk factor due to its direct pathological impact on the fallopian tubes, which play a critical role in the normal implantation of a fertilized egg.