INVESTIGATING FACTORS INFLUENCING CLINICAL PREGNANCY RATES IN HORMONE REPLACEMENT THERAPY FROZEN-THAWED EMBRYO TRANSFER CYCLES: A CROSS-SECTIONAL STUDY

<p style="text-align: justify;">Approximately 50% of embryo transfer cycles are performed as frozen embryo transfer (FET) cycles; however, research on the factors influencing pregnancy rates in these cycles is limited in northern Iran. The aim of this study was to identify the factors influencing the clinical pregnancy rate in hormone replacement therapy (HRT) FET cycles among infertile women. This descriptive-analytical observational study analyzed HRT FET cycles of 429 infertile couples whose embryos were obtained by microinjection at two in vitro fertilization (IVF) centers in Sari, northern Iran, from April 2015 to March 2019. Data were analyzed using SPSS software, version 22, with a significance level set at p < 0.05. The mean ± SD age of women and men was 32 ± 2.52 and 36 ± 1.62 years, respectively. The mean ± SD age of women at the time of oocyte collection was 31.06 ± 5.3 years. Among the 429 patients, 171 cases (39.9%) achieved chemical pregnancy and 156 cases (36.3%) achieved clinical pregnancy. Multivariate regression analysis revealed significant differences between the clinically pregnant and non-pregnant groups (p < 0.05) in factors such as the woman's age at oocyte retrieval, duration of infertility, occupation, body mass index (BMI), developmental stage of the transferred embryo, type of catheter used for transfer, and embryo grade. The study concluded that younger maternal age at oocyte retrieval, shorter duration of infertility, optimal BMI, higher embryo grade, and appropriate selection of transfer techniques are key determinants of achieving clinical pregnancy in HRT-FET cycles. These findings can guide specialists in optimizing FET protocols to improve pregnancy outcomes.</p>