THE EARLIER THE BETTER: INITIAL SERUM HCG LEVELS PREDICT LIVE BIRTH AFTER SINGLE EMBRYO TRANSFER.

To examine how early serum human chorionic gonadotropin (hCG) levels predict live birth (LB) after single embryo transfer (SET). All fresh and frozen embryo transfers between 2002 and 2019 where a single embryo was transferred and a detectable hCG level was confirmed were reviewed. In our practice, serum hCG levels are routinely examined with serum testing done eight days after blastocyst SET (B-SET) and ten days after cleavage stage SET (C-SET). In order to compare hCG levels across IVF cycles where embryos were transferred at different stages, hCG levels were determined in reference to days “after oocyte retrieval (AOR),” which was calculated as the number of days after fertilization. Two hCG parameters were examined to evaluate their relationship with live birth: “reached 100” which was defined as an hCG level of >100 mIU/mL 15 days AOR and “doubled” which was defined as an hCG level that at least doubled over a 48 hour period between the first and second measurements. Analysis of the descriptive statistics was performed. A total of 1397 IVF cycles (1065 patients) where an SET was performed and the initial hCG level was detectable were included in the analysis (82% B-SET and 18 % C-SET). 35% were fresh and 65% were frozen. The mean age at the time of SET was 35.5 years. 62% of cycles where hCG was detectable on first examination ended in LB. In the cycles that ended in LB the median hCG level was 268.4 mIU/mL (interquartile range [IQR] 181.6, 375.0) 15 days AOR. In the cycles that did not end in LB the median hCG level was 56.7 mIU/mL (IQR 18.8, 142.6) 15 days AOR. In cycles where hCG levels only “doubled” the LB rate was 33%, while in cycles where hCG levels only “reached 100” by 15 days AOR the LB rate was 54%. In cycles where hCG levels both “doubled” and “reached 100” by 15 days AOR the LB rate was 84%. In cycles where hCG levels did not “double” or “reach 100” by 15 days AOR the LB rate was 9%. Among cycles that ended in LB there was no relationship between patient age at time of SET and early hCG levels. In those <35, the median hCG level was 121.7 mIU/mL (IQR 86.0, 115.5), in those 35 - 40 the median hCG level was 110.2 mIU/mL (IQR 75.8, 155.8), and in those > 40 the median hCG level was 119.8 mIU/mL (IQR 78.2, 173.8) at mean of 13.4 days AOR. Specific rises in early hCG levels after SET were associated with LB when hCG levels were checked 15 days AOR. In cycles where hCG levels both doubled and reached 100 mIU/mL by 15 days AOR, the LB rate was 84% and this was a stronger predictor of LB than either parameter alone. LB was only achieved in 9% of cycles where hCG levels neither “doubled” nor “reached 100”. Age was not associated with early hCG levels in cycles that ended in LB.