Trends in primeval β-hCG level increment after fresh and frozen-thawed IVF embryo transfer cycles

Mid-trimester beta-human chorionic gonadotropin (BHCG) levels are considerably higher in pregnancies resulting from frozen embryo transfer (FET) compared with fresh (FRET), leading to a higher false positive rate in aneuploidy screening tests. We aimed to investigate the dynamics of BHCG increment and its predictive value for cycle outcome. A retrospective analysis of FRET and FET cycles. BHCG values on days 14 and 16 post embryo transfer were compared and stratified according to the number of sacs demonstrated on US scan at six weeks gestation, and pregnancy outcome (biochemical pregnancy, ectopic pregnancy, spontaneous abortion, and a singleton or twin birth). A prediction model for live birth was built. A total of 430 treatment cycles were analyzed. The average BHCG levels were significantly higher in FET compared with FRET group in nonviable pregnancies on day 14, 450 vs. 183 IU/L, p < .05 and day 16, 348 vs. 735 IU/L, p < .05, respectively. The increment of BHCG was significantly steeper in the FET compared with FRET group in biochemical pregnancies (F = 6.485, p = .012*). Optimal cutoff level for live birth prediction in the FRET group was 211 IU/L (sensitivity 84%, specificity 76.2%) for day 14 and 440 IU/L (sensitivity 86.0% and specificity 72.5%) for day 16. The increment in BHCG differed significantly between the FRET and FET cycles in nonviable pregnancies. Nevertheless, the difference in BHCG levels observed in the second trimester in pregnancies conceived after FRET and FET cycle may begin as early as the fourth week of pregnancy.