Abstract: Objective　 To investigate the effect of oral dydrogesterone alone on endometrial transformation and luteal support in hormone replacement cycles of frozen thawed embryo transfer (FET). Methods　 Two hundred patients under the age of 35 years who underwent FET for the first time after whole embryo freezing for various reasons were randomly selected and divided into control group and observation group with 100 cases for each group. All enrolled patients underwent endometrial preparation with hormone replacement cycles, and endometrial transformation was performed when the endometrial thickness was ≥ 8 mm and serum estradiol (E2) ≥ 549 pmol/L. The observation group received dydrogesterone   20 mg/time, twice/d orally only. The control group received dydrogesterone (10 mg/time, twice/d) orally + vaginal plug by placing progesterone vaginal sustained-release gel 90 mg/d. The cleavage stage embryo transfer was performed 3 d after the conversion of endo-metrium and 5 d after the blastocyst transfer in the 2 groups of patients. From the day of transplantation until 14 days after transplantation, the observation group continued to take oral dydrogesterone tablets 40 mg/d alone, and the control group continued with oral dydrogesterone 20 mg/d + vaginal plugs placed with progesterone vaginal sustained release gel 90 mg/d for luteal support. If the patient was pregnant, luteal support was maintained until 60 days after transplantation. The implantation rate, clinical pregnancy rate, early pregnancy loss rate, satisfaction with medication, adverse drug reactions and cost of medication were compared between the 2 groups. Results　 The implantation rates of patients in control and observation groups were 50.98% (78/153) and 49.34% (75/152), clinical pregnancy rates were 67.00% (67/100) and 65.00% (65/100), and early pregnancy abortion rates were 8.96% (6/67) and 9.23% (6/65), respectively, with no significant differences between the 2 groups. The medication satisfaction was significantly higher in observation group than that of the control group, and the medication cost was significantly lower in observation group than that of the control group (P < 0.05). There was no significant difference in the incidence of adverse drug reactions between the two groups. Conclusion　 In FET with hormone replacement cycle, endometrial transformation and luteal support with oral dydrogesterone alone are safe and effective, which is worthy of clinical promotion and application.

Key words: dydrogesterone, administration, oral, embryo transfer, freeze-thaw embryo transfer, hormone replacement cycle