“…First, endometrial thickness is not the only factor that affects the pregnancy rate since it is influenced by many factors, such as age, endometrial receptivity, and embryo quality ( Zhao et al, 2014 ; Bu and Sun, 2015 ). Second, these studies did not take into account the effect of basal FSH, AMH, AFC, TSH, FT3, blood glucose or the E2 value on the day of the hCG injection per fresh transfer cycle when adjusting for covariates compared with our work, and previous studies have reported that these variables are related to pregnancy rates and miscarriage rates per fresh transfer cycle ( Vaegter et al, 2017 ; Song et al, 2020 ). Third, the research populations are different, and there are physiological differences between ethnic Chinese and ethnic Europeans, the physiological difference between the two ethnic groups are reflected in many aspects, such as body mass index difference, altered ovarian morphology and functional changes, Genes associated with reproduction and fertility changes, which might cause different pregnancy outcomes ( Mura et al, 1991 ; Lachance and Tishkoff, 2013 ; Dumesic et al, 2015 ).…”