a woman can have apparently regular flows and yet still not be having regular ovulation. how can this happen? in a cycle without an ovulation estrogen stimulation (assisted by the hormone fsh) will continue to make the lining of the uterus grow thicker and thicker. in the absence of an lh (luteinizing hormone) surge no ovulation will occur. the progesterone level will not rise. when the follicle that contains the un-ovulated egg involutes (shrinks) the woman’s blood estrogen level will drop. this triggers much of the lining to be shed. thus if it takes two to three weeks for the follicle and un-ovulated egg to regress the woman may have somewhat regular bleeds. how often does this happen? in the first year after menstrual periods begin up to 55% of the cycles may occur without ovulation (mansfield & emans 1984). in a study of 20- to 35-year-old women who had regular cycles but were infertile an average of 30% of women were not ovulating. among these 123 women with regular cycles the highest incidence of not ovulating was 41%. this highest incidence occurred among women who had never had a conception. women who had at least one documented pregnancy had a lower incidence of non-ovulation despite regular periods (hegab 1987). finally the presence of very regular periods accompanied by common premenstrual symptoms (“molimena”) suggests an ovulatory cycle — especially when there are menstrual cramps. yet this may not always be the case. in as many as 5% of these “classic for ovulation” cycles ovulation may not have occurred (speroff 1999).
are regular menstrual periods triggered by regular ovulation?