A case report of twin-chorionic triamniotic triplet pregnancy following single blastocyst transfer in a thin endometrium

Background Endometrial thickness is a key index to evaluate endometrial receptivity, which is closely related to embryo implantation and pregnancy outcome. Thin or damaged endometrium can lead to embryo implantation failure and early pregnancy abortion. It is extremely rare for patients with thin endometrium to have multiple pregnancies. Case presentation A 35-year-old woman with primary infertility for 1 year, thin endometrium caused by chronic endometritis, and combined with a variety of other infertility factors. In the fresh cycle, 8 oocytes were obtained by short-acting long protocol, and 7 embryos were frozen. The fresh cycle transplantation was cancelled due to insufficient endometrial thickness (6.7 mm). The endometrial microenvironment was improved by comprehensive treatment during the resuscitation cycle. After the endometrium was increased to 8.3 mm, the single blastocyst was resuscitated and transplanted, and the triplet pregnancy of double chorionic triple amniotic sac was obtained. After natural reduction, a healthy baby boy was delivered at term. Conclusions Even if single blastocyst transplantation, there is still an unpredictable risk of single oocyte division, which can lead to high-order multiple pregnancy. Clinically, patients should be fully informed of the risk, and closely monitored during early pregnancy. If necessary, selective reduction should be performed in time to improve maternal and infant outcomes.