Scientists are yet to decipher the chemical signals that stop ovarian follicles maturing into eggs when the overall egg reserve becomes low or uncover the role that ovarian cells other than eggs play in this process.
Another surprisingly vague area is why some women (about a quarter) have almost no discernible symptoms while others (another quarter) have hot flushes that are seriously problematic and, in extreme cases, can persist for a decade.
Source: The menopause: why so little research on the middle-aged ovary? | Society | The Guardian