A woman calls the nurse triage line at the OB clinic. She explains that she usually has a 28-day menstrual cycle but that she started bleeding today, a week early, on day 21. The nurse asks the patient if she has had recent intercourse, to which the patient replies, "Yes, seven days ago.”. The nurse asks this because she knows:

The patient likely has a pelvic infection.

The patient may be experiencing implantation bleeding, which can occur 6-10 days following ovulation and fertilization and occurs as a result of the blastocyst burrowing into the endometrium.

The patient may be experiencing secondary amenorrhea, or bleeding between periods.

The patient may be experiencing primary amenorrhea, or bleeding between periods.