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

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.

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

University affiliated private IVF center.

Women undergoing ovarian stimulation between May 2018 and September 2021.

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.

The primary outcome was the difference between FORT-V and FORT-D in their ability to predict the mature oocyte output rate.

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.

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.