Plasma progesterone levels as an index of ovulation

Summary. Plasma progesterone levels were measured in three groups of untreated women. (1) Nine women with follicle rupture, proved by laparotomy or laparoscopy, had values of ≥40 nmol/l on days 18–24 (days −10—5 from the next period); thus a value of <40 nmol/1 should not be taken as evidence of ovulation. (2) Nineteen healthy women with normal menstrual histories had hormone assays on alternate days during one cycle. In five of them all values were <38 nmol/1. (3) Forty women had a single progesterone assay on days 20–29 of a conceptual cycle. Eight of them had a level <40 nmol/l. Ovulation had certainly occurred in all of them, but it is difficult to assess whether the sample timing was optimal since there was no following menstrual period. Progesterone levels in drug-induced conceptual cycles were in general higher than those in spontaneous pregnancy cycles. Women with luteinization of the unruptured follicle frequently had values of >40 nmol/l. Conversely, a secretory endometrium was not uncommon in cycles with values of <38 nmol/l.