A comparison of early pregnancy failure and ongoing pregnancy rates between fresh and frozen embryo transfer following in vitro fertilization.

In order to compare pregnancy outcomes following fresh and frozen embryo transfer after in vitro fertilization (IVF), a retrospective analysis of data from the Royal North Shore IVF Programme was performed. Six hundred and sixty seven embryo transfers following routine IVF were performed during 1991 and 1992. Four hundred and twenty fresh embryo transfers were performed during that period, resulting in a clinical pregnancy rate of 21%. In comparison, 247 frozen transfers, where the initial procedure was routine IVF, were performed, resulting in a clinical pregnancy rate of 16.6%. This difference was not significant. When varying numbers of transferred embryos in the 2 groups were taken into account, there was a significant difference in the proportion of ongoing viable fetuses per embryo returned for 1991, but not for 1992. Although there were a greater number of abortions and ectopic pregnancies in the fresh transfer group, these differences did not achieve statistical significance. The implications of improving results from frozen embryo transfer are discussed.