Your daughter’s situation is called primary ovarian failure, the medical name for when a woman has never had a period. Your motherly intuition is correct in that this does warrant more investigation. Let’s start by looking at what has been done already.
The BCP (“birth control pill”) is generally a combination of a synthetic estrogen and a synthetic progesterone. Normally estrogen builds up the lining of the uterus and progesterone causes development of small blood vessels in that lining to allow implantation and nourishment for a pregnancy. If there is no pregnancy, the progesterone levels drop and the woman has a period. With the use of the pill, the lining is not as thick but she will still have a period at the end of the pill pack. Without estrogen, the lining does not build up and the woman will not have any bleeding. This sounds to be the case for your daughter.
She does not have “withdrawl bleeding” when using just progesterone because she is not making enough estrogen on her own to build up the uterine lining. The pill, however, is providing the estrogen that she is not making. This low level of estrogen needs to be investigated because, as you said, there can be associated health problems.
There are several causes for this situation. Let’s start with what we know. We know that she can have some sort of menstrual flow when both estrogen and progesterone are used but not when progesterone is used alone. This means that there is a uterus and some connection to the outside of the body, however, the function or the level of estrogen is unusually poor. This can be because the ovaries are not making very much estrogen, the signal from the brain center to the ovaries is not working, or the estrogen receptors in the uterus are not responding.
We also know that the vagina may be quite small based on the pelvic exam. Sometimes the development of the vagina (which grows inward to meet the uterus in the embryonic stage) is not complete. This can also be associated with poor development of the uterus and ovaries. The hymenal membrane across the vagina can be covering most of the opening as well.
We also know that the thyroid is normal. In order to further the investigation, I would repeat the pelvic exam using a pediatric sized speculum, get a pelvic ultrasound, and check the blood levels of various hormones that are involved in signaling the brain and the ovaries. Also, a doctor may want to perform a hysterosalpingogram (putting dye into the uterus and tubes) and a laparoscope. These last two procedures are usually done by Ob/Gyn doctors as most family doctors are not trained for them.
These things would help to find why she is not having periods and hopefully find a way to fix the cause. It is important for her health and for future fertility. By the way, while your daughter’s physical activity can contribute to her lack of menstrual periods, it is not the primary cause.
I hope that this information is helpful for you and your daughter!
Gretchen V. Marsh, D.O.