Reduced pregnancy rates following the transfer of human embryos frozen or thawed in culture media supplemented with normal serum albumin

Over a 26 month period 17% of couples having treatment in our clinicalprogrammes selected a commercially available protein (normal serum albumin,NSA) prepared from pooled human sera instead of using their own serum as asupplement for their embryo culture media. In a retrospective analysis of>2000 gonadotrophin-stimulated cycles and 1000 cycles wherefrozen/thawed embryos were transferred, fertilization, embryo quality andpregnancy rates following in-vitro fertilization (IVF), gameteintra-Fallopian transfer (GIFT) or intracytoplasmic sperm injection (ICSI)were unaffected by the type of protein used to supplement the culturemedium. When embryos were thawed in medium containing NSA, both pregnancy(PR) and implantation rates (IR) were significantly lower (P <0.05) thanif the medium was supplemented with serum (PR 8.3% and 17.5%; IR 4.6% and10.5%). Inclusion of NSA before freezing reduced the IR of thawed embryos.To further test this observation all cycles where embryos were cultured andfrozen in medium containing NSA (173 cycles) were matched to cycles whereserum was used and the outcome was compared. At the end of 1995 just overhalf of the embryos in both groups had been thawed. No statisticaldifference was noted in the pregnancy rates (NSA, 5.6% versus serum, 11.3%)but the IR per embryo was significantly lower when embryos were culturedand frozen in medium supplemented with NSA (2.2%) than when serum was usedas the supplement (6.6%).