Perimenopause

Perimenopause is the period of years before menopause, when ovarian function declines and cycles become irregular. It usually lasts several years. Its length varies widely from woman to woman. The staging criteria of the Stages of Reproductive Aging Workshop (STRAW+10) divide it into two parts. In early perimenopause, cycle length begins to vary. In late perimenopause, cycles occur 60 or more days apart. The transition ends 12 months after the final period.¹ Biology, not age, defines the transition. Most women enter it in their mid-forties.

Hormone levels do not simply fall in a straight line during this time. They fluctuate. FSH rises unevenly. AMH falls as the ovaries run low on follicles, the small sacs that hold eggs. Estradiol, the main form of estrogen, fluctuates widely from cycle to cycle and can be high as well as low.² Cycles without ovulation become more common.¹ These fluctuations drive the hot flashes, disrupted sleep, and mood changes that women notice in these years.

Fertility does not end when perimenopause begins. Ovulation still occurs, and pregnancy is still possible. Pregnancy becomes less likely as more cycles lack ovulation and as egg quality declines. Couples who do not wish to conceive need to understand that one missed cycle does not mark the end of fertility. Contraception guidance treats fertility as ended after 12 consecutive months without a period for women aged 50 and older. For women under 50, the window is 24 months. Both thresholds apply when no hormone medication is masking the cycle. The longer window exists because the ovaries can resume function. For couples who wish to conceive, the evaluation differs from the evaluation of younger couples. It gives close attention to ovarian reserve, cycle quality, and the frequency of ovulation. The evaluation includes both partners.