Abstract
Background. There is an urgent need to evaluate the cumulative delivery rate (DR) from a single oocyte harvest after both fresh and frozen embryo transfers (ET). Elective single embryo transfer (eSET) in combination with embryo cryopreservation has reduced the multiple delivery rate (MDR) compared with transfer of two embryos (DET), but the effect of frozen embryo transfers (FET) on cumulative DR and multiple DR has not been evaluated. In cases of imminent risk of ovarian hyperstimulation syndrome (OHSS) fresh ET is not performed and all embryos are cryopreserved. However, little is known about the DR after later frozen ETs from these OHSS cycles. The aim was to find out the total reproductive potential from a single oocyte harvest i.e. DR after fresh transfer and one or several frozen embryo transfers performed after an unsuccesful fresh transfer. The FET cycles performed during 1.3.1998-30.6.2004 were as follows: in the eSET group 907 FETs, in eDET 516 FETs and in no ET 161 FETs. In FET cycles one or two embryos were transferred in the eSET group. The mean number of embryos transferred in FET cycles was 1.5/1.6/1.5 respectively. Methods. All OPU-cycles with ET and/or cryopreservation during 1998-2003. Interpretation. Delivery rate in OPU cycles without cryopreservation was lower than in cycles with cryopreservation. In OPU cycles with cryopreservation the DR was not effected by the number of embryos transferred, but more twins were seen in cycles with eDET than with eSET (26.6% compared to 1.3%). The cumulative DR in the group with eSET in the fresh cycle exceeded that with eDET (52.6% vs 42.8%). In the eSET group only 6.7% of the deliveries were multiples compared to 25% in the group with eDET. Elective SET and cryopreservation is an effective tool not only to achieve a good cumulative delivery rate, but also to reduce multiple births. The possibility to cryopreserve all embryos in case of risk for OHSS is associated with good DR from frozen cycles, since at least one delivery has been achieved in 54.5% of these cycles.