“…Several previous studies (Al-Azemi et al, 2012;Bosch et al, 2010;Huang et al, 2012;Lahoud et al, 2012;Ochsenkühn et al, 2012;Papanikolaou et al, 2012;Wu et al, 2012;Xu et al, 2012) and one recent meta-analysis (Venetis et al, 2013) suggest that elevated progesterone on the day of human chorionic gonadotropin (HCG) (PHCG) administration was associated with adverse pregnancy outcomes in women undergoing IVF and embryo transfer treatment. Our recent study (Liu et al, 2014) confirmed previous observations, and more importantly, we found that elevated progesterone on the day after HCG administration (PHCG+1) was also associated with a decreased pregnancy rate. Our findings were consistent with a recent report in unstimulated cycles, which showed that the progesterone elevation for 2 days or more before the LH surge impaired the clinical pregnancy rate of frozen-thawed embryo transfers in natural cycles, whereas progesterone elevation only on the day of LH surge did not have such an adverse effect, suggesting that serial progesterone measurements around the time of LH surge or HCG administration is more informative than a single measurement (Lee et al, 2014).…”