Premature ovulation after ovarian ultrasonography.

Whereas follicle rupture never occurred before the 37th hour after an ovulatory stimulus (either the onset of the LH surge or hCG administration) in control patients, ovulation was observed at 26 to 36 h in women submitted to ultrasonography during the late follicular phase. Premature ovulation was observed in 5 out of 23 and 8 out of 19 cycles when ultrasonography occurred during the 3 days preceding or in the 36 h following ovulatory stimulus. This as yet unexplained observation leads us to reconsider the advisability of ovarian scan during the late follicular phase of the menstrual cycle.