Ovarian synchrony factor: a new ultrasound parameter in the prognosis of follicular rupture

The present study was carried out to present a new ultrasound parameter used in stimulated cycles and called the ovarian synchrony factor (OSF), which reflects the response of the total follicular cohort. It is calculated from the formula: OSF = (total no. of follicles > or = 16 mm)/(total no. of follicles > or = 10 mm). OSF was determined on the day of human chorionic gonadotrophin (HCG) administration (indicated when at least one follicle was > or = 16 mm) by measuring the widest follicular diameters with an ATL ultrasound apparatus model Ultramark 4, with a 5.0 MHz vaginal transducer, in a total of 221 cycles stimulated for non-invasive assisted reproduction techniques (i.e. no oocyte retrieval). A new ultrasound examination was performed 56-60 h after HCG administration to determine the possible presence of follicular rupture indicated by the disappearance of the follicular image and/or a > 5 mm decrease in the widest follicular diameter. The mean OSF in the group of patients with rupture of at least one follicle (195 cycles) was mean +/- SD, 0.57 +/- 0.25, as opposed to a mean +/- SD of 0.39 +/- 0.25 for the group without follicular rupture (26 cycles). The Mann-Whitney test showed that the OSF of the group with follicular rupture was significantly higher than that detected in the group without follicular rupture (P < 0.01). This information suggests that ovarian stimulation protocols should produce a synchronous follicular response (an OSF as close as possible to 1), i.e. that the follicular lots developing in both ovaries should not vary widely in size. This follicular homogeneity should facilitate the follicular rupture process.