Materials and Methods: In this prospective randomized clinical trial, 100 infertile women younger than 40 years old were randomly divided into intervention (n = 50) and control groups (n = 50). Intervention group received intrauterine injection of 500 IU hCG before frozen-thawed embryo transfer, while control group had the embryo transferred without intrauterine hCG injection. Then, both groups were assessed in terms of implantation, clinical pregnancy and ongoing pregnancy rates. P <0.05 was considered statistically significant.

Results: There was a significant difference in clinical pregnancy rate between intervention (28%) and control (10.4%) groups (P = 0.028, OR: 4.28, CI: 1.25-14.14). The difference in ongoing pregnancy rate between intervention (28%) and control (8.3%) groups was also statistically significant (P = 0.012, OR: 3.44, CI: 1.1-1.18).

Conclusion: Intrauterine injection of hCG (500 IU) before frozen-thawed embryo transfer can significantly improve clinical and ongoing pregnancy in patients with history of in vitro fertilization/intracytoplasmic sperm injection (IVF-ICSI).