Differences between Initial Serum Markers and their Predictive Value in Singleton Pregnancies Conceived after Fresh versus Frozen-Thawed Cleavage Stage Embryos Transfer

Introduction: Initial serum β-hCG level has been shown to be predictive of pregnancy outcome in patients undergoing embryo transfer. .

Aim: To compare initial serum β-hCG levels between singleton pregnancies conceived after fresh versus cleavage stage FET.

Materials & Methods: A retrospective case-control study conducted during January 2004- December 2015. The study cohort included 610 patients in whom either fresh (n=366, 60%) or frozen-thawed (n=244, 40%) day 3 embryos were transferred. β-hCG, estradiol and progesterone levels were measured 14 days after ET. Multiple pregnancies were excluded from this study.

Results: Mean birthweight was s higher in FET pregnancies as compared to fresh ET (3,225 ± 623.4 vs. 3,062 ± 542 respectively, p<0.005). Fetal macrosomia (>4,000 gr) rate was 7.8% vs 1.2% in FET and fresh ET pregnancies, respectively (p<0.001). Low birthweight (<2,500gr) rate was 14.7% vs 9.6% in fresh ET and FET pregnancies respectively (p<0.001). Initial serum β-hCG level was 439 mIU/ml in FET compared with 336 mIU/ml in fresh IVF-conceived pregnancies, (p<0.0001). Estradiol and progesterone levels were lower in FET compared with fresh ET pregnancies (296.2 vs 857 pg/ml and 15.5 vs 37 ng/ml respectively, p<0.0001). Using mixed model, we found that a log increase of initial serum β-hCG levels was associated with 2.6 fold increase in live birth rate (p=0.039).

Conclusion: FET cleavage stage pregnancies are associated with higher initial serum β-hCG and lower estradiol and progesterone levels compared with fresh IVF-conceived pregnancies. Higher initial serum β-hCG levels are associated with increased odds of live birth.