The effect of transferring a low-quality embryo along with a high-quality embryo on the pregnancy outcome

Previous evidence suggests that low-quality embryos may send negative signals to the endometrium and affect the receptivity of the endometrium. This study aimed to evaluate the influence of transferring an additional low-quality embryo with a high-quality embryo on the pregnancy outcome. A total of 1506 fresh embryo transfer cycles between January 2018 and June 2020 were included. The patients were separated into two groups: a single embryo transfer group (SET, patients receiving a single high-quality embryo) and a double embryo transfer group (DET, patients receiving a high-quality embryo and a low-quality embryo). Main outcome measures including multiple pregnancy rate and live birth rate were discussed. Overall, in the primary analysis, patients who receive an additional low-quality embryo improved the live birth by 8.7% and multiple pregnancy rate by 10.0%. In women aged less than 35 years, compared with SET, DET increased the birth rate by 6.0% but resulted in a 13.5% increase in multiples. Women of 35 years above, adding a low-quality embryo increased the live birth rate by only 2.2% but increased multiples by 14.7%. In patients with one cycle of ET, the same results were obtained. In patients with multiple cycles of ET and adding a low-quality embryo, the live birth rate was similar to SET but with a 14.7% increase in multiples. Compared to DET, we prefer to transfer a high-quality embryo. Nevertheless, in women 35 years or older or in patients with multiple cycles of embryo transfer, adding a low-quality embryo did not significantly improve live birth but increased the multiple rate.