In this study, we conducted a retrospective single-centre study of 1664 singleton pregnancies derived from frozen-thawed blastocyst transfer between January 2017 and December 2018. Analysis showed that there were 596 early pregnancy losses and 1068 ongoing pregnancies. We compared serum HCG (human chorionic gonadotophin) concentrations on days 12, 14, 19, and 21, between the pregnancy loss group and the ongoing pregnancy group. The cut-off level of HCG at each time point was calculated to predict pregnancy outcome. Joint analysis of two single HCG levels taken one week apart was carried out to improve predictive accuracy. The levels of HCG at four time points were significantly lower in the early pregnancy loss group than in the ongoing pregnancy group. According to the area under ROC (receiver operating characteristic curve) curves, all levels of HCG taken at four time points showed good ability to predict the outcome of pregnancy. The joint analysis of two single HCG levels taken one week apart further improved the accuracy of prediction.Impact statementWhat is already known on this subject? Multiple studies have shown that the maternal level of serum HCG is the best parameter for predicting the course of pregnancy.What do the results of this study add? The levels of HCG on days 12, 14, 19 and 21 were significantly lower in the early pregnancy loss group than in the group of ongoing pregnancies. According to the area under ROC curves, all levels of HCG taken at four time points showed a good ability to predict the outcome of pregnancy.What are the implications of these findings for clinical practice and/or further research? The joint analysis of two single HCG levels, taken one week apart, further improved the accuracy of prediction.
Keywords: HCG; blastocyst; frozen embryo transfer; ongoing pregnancy; prediction.