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OBJECTIVE To assess whether trophectoderm biopsy has any impact on the level of serum β-human chorionic gonadotropin (β-hCG) in early pregnancies. DESIGN Retrospective cohort study. SETTING University-affiliated reproductive medical center. PATIENT(S) Three hundred and eighty-three women undergoing 396 frozen embryo transfer (FET) cycles with preimplantation genetic testing (PGT), and 353 women undergoing 465 FET cycles with in vitro fertilization or intracytoplasmic sperm injection, all women having positive serum β-hCG results on the 12th day after blastocysts transfers. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) Serum β-hCG levels on the 12th day after warmed blastocyst transfer and perinatal outcomes of clinical pregnancy. RESULTS The diagnostic threshold of serum β-hCG levels on the 12th day after FET for prediction of a live birth was 368.55 mIU/mL with an area under the curve of 0.791 (0.729∼0.853) in the biopsy group, which was lower than the 411.45 mIU/mL in the control group. The average level of serum β-hCG in the biopsy group with clinical pregnancies was statistically significantly lower than that of the control group: 703.10 (569.63) versus 809.20 (582.00), respectively. No statistically significant differences in perinatal outcomes, including gestational age, hypertensive disorder in pregnancy, and neonatal malformation, were found between the two groups. CONCLUSION(S) Trophectoderm biopsy may reduce the level of serum β-hCG in early pregnancies (the 12th day after embryo transfer), but no increased risk was found of adverse perinatal outcomes after trophectoderm biopsy.