A new term for the normal cessation of female fertility up to 10 years before the menopause, being apparent in some women after the age of 33 and most women by 45. Different from the perimenopause, which occurs as egg numbers fall far enough to cause shortening of the menstrual cycle, particularly the follicular phase, and accompanied by elevation of serum FSH when measured during menstruation. If pregnancies are attempted through the oopausal transition, a woman who has had no prior reproductive disturbance will typically experience recurrent miscarriages before developing otherwise unexplained infertility, manifesting in the IVF lab sequentially with unexplained implantation failure of apparently satisfactory embryos, then, in turn, a decreased rate of forming blastocysts, defective cleavage, and then failure of fertilisation. There is no known method of overcoming its effects short of egg donation, except for some hope that the procedure of cytoplasmic transfer might be helpful.

The natural process in which the older the female fetus, girl or woman gets the fewer are the eggs (as primordial follicles) left in the ovaries; the huge majority of eggs are lost because of atresia, only a tiny fraction by ovulation. Before the eggs are depleted there is a mild or moderate elevation in serum FSH when measured during the menstrual phase (often called a day 3 FSH. When the eggs are more or less depleted there will be primary ovarian failure and, in women who have had periods, the menopause will take place, perhaps prematurely (premature menopause). Infertility, however, usually precedes total egg depletion by up to 10 years. See also mitochondrion and oopause.

A time of intermittent symptoms of the menopause that first becomes apparent as egg numbers in the ovaries fall far enough to cause shortening of the menstrual cycle, particularly the follicular phase, and accompanied by elevation of serum FSH when measured during menstruation. As it progresses, menstrual cycles can shorten considerably, while becoming interspersed unpredictably by unusually long cycles, sometimes producing cystic follicles and even anovulatory dysfunctional bleeding, as well as episodes of hot flashes. Different from the oopause.