Volume-based follicular output rate improves prediction of the number of mature oocytes: a prospective comparative study.

Objective: To test whether volume-based follicular output rate (FORT-V) is superior to diameter based follicular output rate (FORT-D) in predicting the number of mature oocytes. The follicular output rate (FORT) is the ratio between preovulatory follicle count (PFC) and antral follicle count (AFC) and has been proposed as a better predictor of the ovarian response compared with AFC alone.

Design: A prospective observational study of 215 consecutive women (80 oocyte donors and 135 in vitro fertilization [IVF] patients) undergoing ovarian stimulation for IVF.

Setting: University affiliated private IVF center.

Patient(s): Women undergoing ovarian stimulation between May 2018 and September 2021.

Intervention(s): Manual two-dimensional ultrasound and computer-generated (three-dimensional ultrasound, [3D]) AFCs were performed at baseline. During ovulation induction, follicular growth was monitored in each patient using both two-dimensional and 3D ultrasound. Preovulatory follicles were defined as those with a mean diameter of 16-22 mm. The trigger was based on the follicular volume according to our standard protocol: at least 2 follicles with a volume of >2 cc with 70% of the follicles having a volume of >0.7 cc.

Main Outcome Measure(s): The primary outcome was the difference between FORT-V and FORT-D in their ability to predict the mature oocyte output rate.

Result(s): In both IVF patients and oocyte donors, the computer-generated AFC was greater than the manual AFC. The FORT-V was higher than the FORT-D for both computer-generated (the difference was 35 [95% CI {confidence interval}, 32-45] in oocyte donors and 21 [95% CI, 5-46] in IVF patients) and manual FORT (the difference was 38 [95% CI, 32-45] in oocyte donors and 15 [95% CI, 3-43] in IVF patients) and was closer to the mature oocyte output rate. There was a direct correlation between the computer-generated AFC and the PFC based on volume and between PFC based on volume and the number of mature oocytes in oocyte donors and IVF patients.

Conclusion(s): In this prospective study of 215 women, the FORT based on 3D ultrasound derived follicular volume (FORT-V) was superior to the FORT-D in determining the ovarian response in both oocyte donors and IVF patients. Moreover, our results support the non-inferiority of the computer-generated method compared with the manual method for the determination of AFC. Further studies on the role of computer-generated antral follicle characteristics may be useful in evaluating follicle stimulation regimens.