Ultrasonographic morphology of the human preovulatory follicle wall prior to ovulation

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Abstract
Morphologic changes in the walls (stratum granulosa and theca interna and externa) of preovulatory follicles were studied in 15 clinically normal women. Ovulation was visualized in 11 of 15 (73%) women. Images were recorded using high‐resolution transvaginal ultrasonography. Mean follicular diameter immediately before ovulation was 20.7 ± 0.6 mm. Echoes representing the cumulus oophorus/oocyte complex were observed in 10 of 11 (91%) follicles for which ovulation was ascertained. Thickness of the deep internal wall increased (P < 0.02) beginning from 4 to 5 h before ovulation. The apical wall thinned (P < 0.0001) to nondetectable limits immediately before follicular rupture. Four women (27%) did not ovulate during the imaging period [34–41 h post‐human chorionic gonadotropin hCG]. The four follicles that did not ovulate remained of uniform thickness; stigma formation was not observed. The data supported the hypothesis that ultrasonographically detectable alterations in preovulatory follicles precede ovulation. Clinical applications include prediction of the potential for, and interval to, rupture of the preovulatory follicle and timing of ova retrieval in women undergoing ovarian stimulation for amelioration of infertility.