JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):210
Poster Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263873

P-198. Reproductive Outcomes of Endometrial Preparation for Em bryo Transfer: A Retrospective Cohort Study Comparing Modified Natural and Hormone Replacement Therapy Cycles

Luma Soares Fagundes¹, Ana Márcia de Miranda Cota², Laura Caetano de Sá¹, Rívia Mara Lamaira²

¹ Faculdade Ciências Médicas de Minas Gerais – Belo Horizonte – MG - Brasil
² Hospital Mater Dei Santo Agostinho – Belo Horizonte – MG - Brasil

Objective: Is there an endometrial preparation protocol for embryo transfer associated with better reproductive outcomes? The main objective of this study is to analyze the different approaches to endometrial preparation for embryo transfer, exploring the potential influence of the modified natural cycle (mNC) and hormone replacement therapy (HRT) protocols on reproductive outcomes.
Methods: This is a retrospective, observational cohort study conducted in the Human Reproduction Department of a hospital in Minas Gerais. Data were collected through medical record analysis of patients who underwent embryo transfer between 2020 and 2024. A total of 180 cycles using mNC or HRT protocols were included. All patients were undergoing in vitro fertilization or intracytoplasmic sperm injection cycles and were recruited regardless of the controlled ovarian stimulation protocol used. Patients were eligible regardless of age, race, ethnicity, race, sexual orientation, or socioeconomic status. Qualitative variables were summarized as frequencies and percentages, and continuous variables as medians with interquartile ranges. Associations between qualitative variables were tested using Fisher's Exact or Chi-square test, and nonparametric tests were applied to quantitative data. A p-value<0.05 was considered statistically significant. The research protocol was approved by the Research Ethics Committee (CAAE: 82748624.9.0000.5128; Opinion No. 7.042.050).
Results: A total of 180 cycles were analyzed (69% HRT; 31% mNC). The mean age at oocyte retrieval was 38 years, with no significant age differences between groups. Endometrial thickness was comparable (p=0.4), indicating adequate endometrial development under both protocols. There were no significant differences in the prevalence of genetic disorders (p=0.059), tubal factor infertility (p=0.076), advanced maternal age (p=0.5), uterine myomatosis (p=0.3), or male factor infertility (p=0.2). However, endometriosis (p=0.029) and unexplained infertility (p<0.001) were more common in the mNC group, which also showed a longer duration of infertility (median 5 years vs. 3 years; p=0.003). Anovulation was more frequently observed in HRT (p=0.006). Most transfers occurred at the blastocyst stage (75%), with similar distribution between groups (p=0.4). The number of embryos transferred did not differ significantly (p=0.6). Laboratory variables, including embryo developmental stage, PGT-A testing, and progesterone levels on transfer day, were also balanced across groups. The overall β-hCG positivity rate was 40% in the HRT group and 38% in the mNC group (p=0.8). Clinical pregnancy rates were similar (35% in HRT vs. 34% in mNC; p>0.9). The number of gestational sacs was likewise comparable: 33% of patients in both groups had singleton sacs, while twin sacs were observed in 5.6% of HRT and 3.6% of mNC cycles (p>0.9). No significant differences were identified in miscarriage (4% vs. 1.8%) or ectopic pregnancy rates (0.8% vs. 1.8%) between groups (p=0.8).
Conclusion: Both mNC and HRT endometrial preparation protocols demonstrated comparable clinical outcomes in embryo transfer cycles. The mNC protocol may be a suitable alternative for patients with regular ovulatory cycles, offering a physiological and less medicated approach, while the hormonal replacement therapy protocol remains advantageous for those requiring greater control and scheduling flexibility. However, the retrospective design, potential selection bias, small sample size in the mNC group, and lack of live birth and obstetric outcome data limit the findings. Protocol choice should be individualized, considering patient characteristics, clinical indications, and treatment logistics. Prospective randomized trials are needed to confirm these results and assess long-term outcomes.