As has been said elswhere on the site, premature ovarian failure (POF) is a condition that used to be called "premature menopause."  It's marked by post-menopausal hormone levels and no periods (amenorrhea) ocurring before the age of 40.

While it's similar to menopause, it's not strictly menopause.  There are several key differences.  One of the most important differences is that many women with POF can and do still ovulate from time to time and can even get pregnant.  (According to statistics, this occurs to roughly 8 to 10% of women with POF.)

This is because POF doesn't necessarily mean lack of viable follicles.   Yes, some women with POF do have early depletion of follicles (which is then, in effect, menopause).  But others -- nearly half according to some experts -- actually still have follicles.   The problem in this case is a "disconnect" between hormones and ovarian function or an autoimmune problem.  

Premature ovarian failure -- as with many conditions -- develops over time.  Prior to full-blown POF (i.e. no periods for at least 4-6 months and post-menopausal hormone levels), you move through different stages  through what's now called "primary ovarian insufficiency" (POI),

Specialists have identified four stages of POI that culminate in POF.

• Stage 1 Primary Ovarian Insufficiency:  This is the beginning stage, in which you still have a normal FSH level, but are infertile -- and don't respond to infertility treatments using FSH to cause superovulation.
• Stage 2 Primary Ovarian Insufficiency: In this case, your FSH level is higher -- and you still don't respond to FSH therapy during IVF.
• Stage 3 POI:  This is the point just before POF -- when your FSH levels are higher, you are getting symptoms (particularly changes in your menstrual cycle -- such as skipped periods (known as "oligomenorrhea"); overly frequent preriods ("polymenorrhea"); bleeding in between periods ("metorrhagia"), not just light spotting, but rather heavy bleeding).   Because your FSH levels have increased, it's common to have other symptoms beyond the changes in your period, such as hot flashes, night sweats and vaginal dryness.
• Stage 4 -- or POF:  At this point, you've moved into premature ovarian failure.  Your hormones test at post-menopausal levels and you cease having a period (amenorrhea).

Okay...so that's the technical breakout of what happens, how POI becomes POF.  And it all seems nice and neat.  But, as you might expect, it's not quite as cut and dried as it sounds.  Typically, the first sign that you're entering POI (and thus POF) is a change in your menstrual cycle.  Your cycles may shorten -- you get your period more frequently.  But in other cases, your period seems completely normal.  The tip-off could simply  be that you're unable to get pregnant and there appears to be no reason. And for some women, the first tip-off is hot flashes -- even though they're still cycling normally.  The latter point is a key one:  Unlike "normal" menopause, women with POF often exhibit symptoms linked with very low estrogen even while they're still getting regular periods.  It's this that often confounds doctors who aren't familiar with this condition -- and can lead to problems for you, the patient.

Because there is this continuum of stages, it's important -- especially if you want to get pregnant -- to determine what is going on with your body if you do notice changes in your cycle or other symptoms.  Simply being told that it's perimenopause or something else, going on the pill to regulate your cycle and ease symptoms and so forth might possibly be one of the worst things you can do...because as the ovarian insufficiency progresses, you will wind up less likely to be able to pursue that pregnancy.