Size matters: breaking the decades-old dogma of universal follicle size for timing egg retrieval

Is the routine practice of triggering ovulation at a fixed follicle size (18-22 mm) in IVF optimal across all age groups?

An analysis of 109 autologous IVF cycles with fresh embryo transfer performed in 2025 was undertaken at the authors' New York fertility centre, following the approach of trigger-timing optimization from a 10-year experience with the Highly Individualized Egg Retrieval (HIER) protocol. HIER is based on the longitudinal understanding of age-related changes in follicular dynamics and oocyte maturity, involving lowering follicle size thresholds for triggering with advancing ovarian age - often to less than 12-14 mm in patients over 43 years of age - combined with routine rescue in-vitro maturation (rIVM) of all immature oocytes. The main outcome was clinical pregnancy rate, both global (median age 42.8 years, range 26.6-51.9 years) and over age 43 (median age 46.9 years, range 44.0-51.9 years), a decade after implementation of HIER with rIVM.

In 2025, a 12% overall clinical pregnancy rate per transfer was achieved in women with a median age of 42.8 years, and 8% in the subset of patients aged 44 years or older.

The universal application of a fixed follicle size (18-22 mm) for ovulation triggering may be outdated. Age-adjusted protocols such as HIER optimize IVF success, especially in older or poor-prognosis patients in whom there tends to be a rapid acceleration of premature luteinization. This warrants further validation for broader clinical adoption.