Which of the following is a cause of secondary amenorrhea:

Normal ovaries are extremely sensitive to radiotherapy hence pelvic irradiation, given for various pelvic malignancies may cause secondary amenorrhea by causing ovarian failure. Otherwise, the more common causes of secondary amenorrhea in women are pregnancy, polycystic ovarian syndrome, hyperprolactinemia, tuberculosis, uterine synechiae, premature ovarian failure and hypothalamic dysfunction. Pregnancy must be considered in all women of reproductive age with amenorrhea.