Background: Nowadays, there is no universal criteria for trigger time during controlled ovarian hyperstimulation (COH). Particularly, in the so-called GnRH-a prolonged protocol, widely used in China, the ideal time to trigger ovulation is not yet well defined.
Methods: This was a large-sample retrospective analysis. Between January 2016 and January 2020, 1,925 young patients who underwent their first in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) cycles with normal ovarian response were divided into three groups based on their dominant follicular proportions (DFP, defined as ≥18 mm follicles /≥14 mm follicles; Group A: < 30%; Group B: 30% - 60%; Group C: ≥ 60%). Binary logistic regression and multivariate linear regression were used to assessed whether DFP levels were related to clinical pregnancy, number of blastocysts frozen, blastocyst formation rate and low blastocysts frozen.
Results: Binary logistics regression analysis showed that compared with Group A, the OR for clinical pregnancy was 1.345 in Group B (P = 0.023); however, there was no statistical difference between Group C and Group A (P = 0.216). On one hand, multivariate linear regression analysis indicated that DFP was negatively associated with number of blastocysts frozen (β ± SE: Group B vs Group A = -0.319 ± 0.115, P = 0.006; Group C vs Group A = -0.432 ± 0.154, P = 0.005) as well as blastocyst formation rate (β ± SE: Group B vs Group A = -0.035 ± 0.016, P = 0.031; Group C vs Group A = -0.039 ± 0.021, P = 0.067). On the other hand, compared with group A, the OR for low blastocyst frozen was 1.312 in Group B (P = 0.039) and was 1.417 in Group C (P = 0.041).
Conclusions: Excessive delay of trigger in GnRH-a prolonged protocol might reduce the developmental potential of oocytes and reduce the number of available blastocysts, which might result in a lower cumulative pregnancy rate. But further confirmation by strict prospective randomized controlled study should be needed.
Trial registration: https://clinicaltrials.gov/; NCT03305510; Registered 08 October 2017 - Retrospectively registered.