Evaluating the role of follicular output rate in clinical and embryological outcomes in IVF: a prospective study

To examine the association between follicular output rate (FORT) and embryological and clinical outcomes, including live birth rate, in patients undergoing in vitro fertilization (IVF).

This prospective cohort study enrolled 166 patients undergoing IVF between October 2023 and January 2025. FORT was calculated as the ratio of pre-ovulatory follicles (16–24 mm) on trigger day to baseline antral follicle count (AFC; 3–9 mm), multiplied by 100. Patients were stratified into low, medium, and high FORT tertiles, and FORT was also evaluated as a continuous variable in multivariable logistic regression. An exploratory receiver operating characteristic (ROC) analysis was performed to assess discriminatory performance and to identify a data-derived reference threshold. All analyses were conducted separately for non-PCOS and PCOS cohorts.

In non-PCOS patients (n = 136), the number of oocytes retrieved, mature oocytes, and good-quality embryos differed significantly across FORT tertiles (all p < 0.05). Clinical pregnancy rates were 14.9%, 27.8%, and 37.2% in the low, medium, and high FORT groups respectively (p = 0.045), with corresponding differences in live birth rates (p = 0.049). On multivariable analysis, FORT (OR 1.04; 95% CI 1.002–1.079; p = 0.039) and the number of available embryos (OR 1.35; 95% CI 1.082–1.676; p = 0.008) remained independently associated with clinical pregnancy. Exploratory ROC analysis yielded an AUC of 0.607 (95% CI 0.52–0.69). A data-derived reference threshold of FORT at 64.2% was associated with higher clinical pregnancy rates compared with lower FORT values (40.9% vs. 23.3%; p = 0.030; OR 2.27, 95% CI 1.14–4.55). No significant associations were observed in the PCOS subgroup, though this analysis was limited by small sample size (n = 30).

FORT is significantly associated with embryological and clinical pregnancy outcomes, including live birth, in non-PCOS IVF patients. As a cycle-specific functional measure of follicular responsiveness, FORT may complement static ovarian reserve markers for counselling and outcome stratification. FORT values in the higher range (approximately ≥ 65%) were associated with improved clinical pregnancy rates, but the limited discriminatory performance of the ROC analysis underscores the need for external prospective validation of this cutoff before any clinical implementation.