Successful pregnancy and live birth despite discontinuation of hormone replacement therapy at 3 weeks and 5 days of gestation following vitrified-warmed embryo transfer under a hormone replacement therapy cycle: a case report and literature review

Abstract Background In freeze–thawed embryo transfer (FET) cycles, hormone replacement treatment (HRT) is crucial for implantation and pregnancy maintenance. HRT typically continues until the 10th week of pregnancy owing to a luteoplacental shift, although a definitive HRT regimen remains undetermined. We present the case of a woman who underwent FET during an HRT cycle and ceased HRT after a negative pregnancy test at 3 weeks and 5 days, who went on to deliver a healthy baby. Case presentation A 30-year-old Japanese woman with primary infertility was scheduled for FET. Estrogen supplementation was initiated as part of the HRT cycle for endometrial preparation. After achieving an endometrial thickness of 8 mm, progesterone supplementation was commenced, and the transfer of a 4BB blastocyst occurred 5 days after initiating progesterone treatment. At a gestational age of 3 weeks and 5 days, her serum human chorionic gonadotropin (hCG) level was only 8.3 mIU/mL, leading to discontinuation of HRT due to the absence of pregnancy. However, at 6 weeks and 1 day, her serum hCG levels significantly rose to 9359 mIU/mL, prompting the resumption of HRT. Ultrasonography confirmed the presence of a gestational sac and cardiac activity in the uterus, and HRT was continued until the 10th week. Ultimately, she delivered a healthy female neonate vaginally, weighing 2601 g at 40 weeks and 6 days. Conclusions Progesterone supplementation is customary in FET with HRT cycles, although it has raised the possibility that there is demonstrating the potential for an ongoing pregnancy and resulting in a healthy baby under no progesterone replacement prior to the luteoplacental shift in this case. The duration and dosage of progesterone in luteal support for FET with HRT warrant further investigation.