Objective: To explore the risk factors associated with twin pregnancy in double embryo transfer.
Methods: A retrospective analysis was performed for 2970 double embryo transfer cycles, including 1984 cycles of fresh embryo transfer and 986 cycles of frozen-thawed embryo transfer (FET). Multiple factor Logistic regression was used. The twin pregnancy rate was studied in group of age < 35 or age ≥ 35 years old, in group of zero, single or double high-quality embryos transferred and group of fresh embryo transfer or FET cycles.
Results: (1) There was a significantly negative correlation between women's age and twin pregnancy according to the analysis of multiple factor Logistic regression (P < 0.01). And a significantly positive correlation existed between the number of high-quality embryos transferred, FET and twin pregnancy (P < 0.01); (2) the twin pregnancy rate of both fresh embryo transfer and FET cycles was higher in group of age < 35 years than that in group of age ≥ 35 years (16.0% vs 8.0%, P < 0.01; 26.9% vs 14.2%, P < 0.01); (3) the twin pregnancy rate of fresh embryo transfer cycles with double high-quality embryos transferred was higher than that with zero or single high-quality embryos transferred (19.1% vs 5.4%; 19.1% vs 11.0%, P < 0.01); the twin pregnancy rate of FET cycles with double high-quality embryos transferred was also higher than that with zero or single high-quality embryos transferred (32.7% vs 10.8%; 32.7% vs 20.7%, P < 0.01); (4) the twin pregnancy rate of FET cycles was significantly higher than that of fresh embryo transfer cycles (24.7% vs 14.9%, P < 0.01).
Conclusion: Women's age, the number of high quality embryos transferred and FET are risk factors associated with twin pregnancy. At reproductive centers with a mature technique of FET, we recommend performing single high-quality embryo transfer in FET cycles to reduce the occurrence of twin pregnancy.