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

A previous chlamydia infection is indeed a well-known risk factor for ectopic pregnancy. Chlamydia is a sexually transmitted infection that can lead to pelvic inflammatory disease (PID), which in turn can cause scarring and damage to the fallopian tubes. This damage increases the likelihood that a fertilized egg will implant in the fallopian tube rather than the uterus, resulting in an ectopic pregnancy.

Natural delivery does not confer any increased risk for ectopic pregnancy; it is related to factors that affect the reproductive system's anatomy and function. Routine gynecological exams are essential for women's health, but they do not directly influence the risk of having an ectopic pregnancy, nor do they act as a risk factor. Hence, the correct identification of a previous chlamydia infection as a risk factor highlights the importance of managing and treating sexually transmitted infections to reduce the likelihood of ectopic pregnancies.