Which among the following is the commonest site of ectopic pregnancy?

Nearly 95 percent of ectopic pregnancies are implanted in the various segments of the fallopian tubes. Of these, most are ampullary implantations, followed by the isthmus. The remaining 5 percent implant in the ovary, peritoneal cavity, or within the cervix. Because the tube lacks a submucosal layer, the feilized ovum promptly burrows through the epithelium, and the zygote comes to lie near or within the muscularis. The rapidly proliferating trophoblast may invade the subjacent muscularis. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 10. Ectopic Pregnancy. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.