As outlined in the previous section, fertility begins to decline in the late reproductive years and continues to decline until menopause occurs and a woman is considered to be infertile. The point at which pregnancy becomes difficult, but not impossible, is referred to as either diminished ovarian reserve (“DOR”) or poor ovarian reserve. DOR is a natural phase that all women pass through on their way to menopause. Here is an excellent article that further explains what happens in DOR.
It’s important to note that the reproductive phases outlined previously and the entry into
DOR do not occur on a fixed timetable. Although the majority of women will fall into the
timeframes outlined above, some women are exceptions and their fertility may be reduced
prematurely, even in the absence of premature ovarian failure. The causes for this early
decline in fertility are generally unknown.
High FSH is one factor that can point to DOR. When FSH approaches and exceeds the cutoff in most clinics (ranges from around 12 to 15), and if other indications are present, then a woman may be diagnosed with DOR. Women with DOR have an increased likelihood of having difficulty conceiving and being a “poor responder” – i.e., responding poorly or not at all to fertility drugs which are meant to improve a woman’s chances at pregnancy.
Having multiple factors pointing to a diagnosis of DOR increases the likelihood of DOR.
This is particularly important in younger women with prematurely high FSH because the FSH can be elevated but if other factors are good, then the odds of conception are better.
Below is a list of other factors besides high FSH that can point to a diagnosis of DOR:
- Low antral follicle count. Antral follicles are follicles that are “in the running”,
so to speak, to be the ovulated follicle for a particular month. In a natural cycle,
generally one follicle gets chosen and ovulated and the other ones that aren’t chosen
die off. In an ART cycle, the medications attempt to recruit multiple follicles from the
antral pool, thus improving the chances of conception. If there are fewer antral follicles, this is an indication that the number of remaining eggs in the ovaries is reducing – i.e., it points to DOR. The number of antral follicles can be determined via ultrasound.
- Low Inhibin B. Inhibin B is produced by the antral follicles and so if there are fewer
antral follicles then the Inhibin B level will be lower. Inhibin B is tested via a blood test.
- Smaller ovarian volume. The ovaries reduce in size as the reserve of eggs diminishes
over a woman’s lifetime. Ovarian volume can be measured via ultrasound.
- Low Anti-Mullerian Hormone (AMH). AMH can be measured via a bloodtest.
- Clomiphene-Citrate Challenge Test (CCCT aka Clomid Challenge Test). The CCCT measures how well the ovaries respond to Clomiphene-Citrate – a stimulating medication.
High FSH does not preclude pregnancy. High FSH indicates that a woman is likely to be a poor responder to fertility medications. It does not necessarily mean that there aren’t any high quality eggs remaining and that pregnancy is impossible. It MAY mean that it will take a long time for her to become pregnant and that IUI/IVF may or may not increase her chances of pregnancy, depending on the protocols used. If a young woman has prematurely high FSH, this woman MAY or MAY NOT suffer from premature ovarian failure or premature menopause.
High FSH can be caused by other factors besides DOR. Your RE should rule out other potential causes for high FSH before diagnosing you with DOR. Other causes are unusual but should be investigated nonetheless. FSH can rise due to autoimmune disorders, adrenal gland impairment, hereditary dizygotic twinning, discontinuing the use of oral contraceptives (FSH can rise temporarily after extended use of contraceptives), lactation, unilateral ovariectomy, recovery from hypothalmic amenorrhea and excessive smoking.