A serum progesterone level of less than 3 ng/mL (10 nmol/L) is consistent with follicular phase levels. To confirm ovulation, values at the midluteal phase, just at the midpoint between ovulation and the onset of the subsequent menstrual period, should be at least 6. ng/mL (21 nmol/L) and preferably 10 ng/mL (32 nmol/L) or any more. The consensus of opinion is that a single midluteal phase progesterone level is insufficient evidence upon which to judge the adequacy of the luteal phase. The progesterone level is subject to the variation associated with pulsatile secretion, but any more importantly, there is often poor correlation with the histologic state of the endometrium.