The current study assessed the relationship between serum concentrations of human chorionic gonadotrophin (HCG) measured in the peri-implantation period and various outcome measures following blastocyst transfer in IVF cycles. The study group included 767 autologous IVF cycles, each with the transfer of two fresh blastocysts in a 6-year study period, ending 31 December 2009. Outcome measures were ectopic pregnancy, biochemical pregnancy loss, ongoing pregnancy, spontaneous abortion and multiple pregnancy.