Dear ConcernedHealth: The most clear answer first, OK? With a lifetime of irregular and heavy periods chances are good that you have a pattern of irregular or absent ovulations.
Simply stated, if the uterine lining is like grass or lawn, estrogen is like the fertilizer (causes a thickening of the lining ), and progesterone is like the lawnmower (keeps the lining thin by three different mechanisms). This is why DepoProvera (high dose synthetic progesterone) brings about a thin lining, and why birth control pills (relatively progesterone dominant) bring about shorter, lighter periods. It is also why women who miss ovulations (no progesterone produced) are at a greater risk for a too thick lining and endometrial cancer. My youngest patient to have cancer of the uterine lining was 26 and she had a menstrual history similar to yours.
A too thick lining ("endometrial hypertrophy") is a common cause of heavy and prolonged bleeding. The diagnosis can be made by ultrasound or endometrial biopsy. The ultrasound image measures the thickness of the lining ("endometrial stripe"); with hypertrophy it is usually more than 12-15 mm. I had another patient once with a stripe of 30mm! The endometrial biopsy takes a sample of lining tissue and the pathologist can then make a very accurate diagnosis base upon the cells seen under the microscope. The treatment for simple hyperplasia/hypertrophy which does not contain abnormal cells is synthetic progesterone pills or shots. This shrinks down the too thick lining.
My best GUESS Is that the lining of your uterus is thick (not the actual muscular wall of the uterus). Your GYN is being very thorough and showing careful concern about a thick lining in the presence of your menstrual history. As you have read above, one need to rule out any abnormal or precancerous cells in a too-thick lining. This requires a sample of tissue (eg in office endometrial biopsy or D&C). If there are no abnormal cells use of birth control pills or other hormones is appropriate. But if abnormal cells are present (hopefully not in your case) then other treatments may be indicated. In my clinical OPINION, I would concur with your GYN. You might be able to find another GYN who would give birth control pills---but wouldn't rather have any abnormal cells ruled out?
In Support,
Jane