Frequency, sequence, and side of ovulation in women menstruating normally.

SHORT REPORTS Frequency, sequence, and side of ovulation in women menstruating normally Ovulation in the primate is usually regarded as a consistently alternating process that occurs with equal frequency in the right and left ovaries. We investigated whether ovulation in women occurs with equal frequency in each ovary, alternating consistently between the ovaries. Subjects, methods, and results Sixteen women ovulating normally who were awaiting donor insemination participated in the study. Pelvic ultrasonography was performed with a real time sector scanner (Advanced Diagnostic Research 4000 S/L) at least once during each cycle as close as possible to the day when basal body temperature was lowest. Ovulation was confirmed by records of biphasic basal body temperature, mean duration ofluteal phase of 14 (SEM 2) days, and a mid-luteal plasma progesterone concentration-38-4 nmol/l (12 ngtml). Statistical analysis was based on the Bernolli distribution, assuming that in normal circumstances there is a 50% chance of ovulation occurring in either ovary. A total of 97 follicles was observed in 16 women during 90 cycles. In seven cycles (8%) two follicles were observed, always in the same ovary. Of the 97 follicles, 62 (64%) were detected in the right and 35 (36%) in the left ovary (p<0-01) (table). Alternation of side of ovulation in at least four consecutive