Embryo transfer day does not affect the initial maternal serum β-hCG levels: A retrospective cohort study

The aim of this study is to compare the serum β-hCG values post transfer of a cleavage stage embryo versus a blastocyst stage embryo at equal time intervals post oocyte retrieval (OR) in clinically pregnant patients, and to ascertain a β-hCG value to predict pregnancy outcomes. This is a retrospective cohort study of 560 women with clinical pregnancy who underwent an embryo transfer performed at either the cleavage stage or the blastocyst stage of embryo development between January 2003 and June 2014 at the Center for Assisted Reproduction (CARE), Singapore General Hospital. The serum β-hCG level was measured on day 17 post OR. The β-hCG values were not significantly different in the cleavage stage versus the blastocyst stage embryos (mean±SD: 387±486IU/L D3 vs. 352±268IU/L D5, p=0.96, median value 297 in both groups). Our study suggests that the initial maternal serum β-hCG values were not affected by the day of transfer of the embryos since assessing the β-hCG at equivalent points after transfer should not lead to a significant difference assuming the progress and development of the embryos occurred as expected.