Strengths and Limitations
Compared with previous studies,14, 15 the study had
some advantages in its design that afforded strong confidence on the
results. Firstly, the study was based on a large sample including 9832
FET cycles. Then, in order to eliminate the effects of the embryo
quality on the clinical outcomes in this study, we selected the FET
cycles that the two embryos after thawed were good-quality embryos.
Moreover, the study divided the female age into three groups to decrease
the effects of female age on clinical outcomes. Furthermore, the study
selected first FET cycle and excluded FET cycles with abnormal uterine
to ensure the accuracy of data. One limitation of this study was that
patients’ characteristic of the number of oocytes from the OPU was not
mentioned.