Luteal Phase Support in in vitro Fertilization at 2,800 Meters above Sea Level: Micronized Progesterone versus Combination with Dydrogesterone

Objective: To evaluate the effectiveness of luteal phase support with micronized progesterone alone versus micronized progesterone plus dydrogesterone in patients undergoing in vitro fertilization (IVF) at a human reproduction center located 2,800 meters above sea level. Methods: Retrospective observational study conducted between July 2021 and January 2025 at Hospital Provida (Latacunga, Ecuador). A total of 113 patients with endometrial thickness ≥ 7 mm and serum progesterone < 1 ng/mL before embryo transfer were included. Group 1 received micronized vaginal progesterone 400 mg every 12 h; Group 2 received the same dose plus oral dydrogesterone 10 mg every 12 h. Primary outcomes were biochemical pregnancy (positive β-hCG, defined as ≥ 5 mIU/mL) and clinical pregnancy (fetal heartbeat). Results: Of the total, 40 patients were assigned to Group 1 and 73 to Group 2. Mean age was 38.4 vs 37.7 years, with no significant baseline differences. Biochemical pregnancy rates were 62.5% (monotherapy) and 56.2% (combination), while clinical pregnancy rates were 60.0% and 57.5%, respectively (p > 0.05). Conclusion: Luteal phase support with micronized progesterone alone showed a trend toward higher biochemical and clinical pregnancy rates compared with the combined therapy. These findings support the importance of individualizing luteal phase support strategies in IVF, particularly under physiologically challenging conditions such as high altitude.