The Occurrence of Ovulation at the Midcycle

It is commonplace for gynecologists to refer to "midcycle" ovulation of women. This concept has often led to the routine diagnosis of ovulatory status on day 14 of what is expected to be a 28-day menstrual cycle. For example, the postcoital test in an infertile patient, or intercourse to achieve pregnancy in a normally fertile patient, is often timed around day 14 under the assumption that ovulation is occurring then. Advocates of natural family planning (NFP) have criticized the concept of "midcycle" ovulation, because their clinical experience suggests that the natural irregularity of menstrual-cycle length militates against ovulation's occurring with any great frequency on day 14. This report analyzes the relationship of day 14 and the actual midcycle of the menstrual cycle to each other and to indirect hormonal parameters that more directly estimate the time of ovulation.