Counselling on cryopreservation of pronucleated oocytes.

The German Embryo Protection Law permits only the cryopreservation of supernumerary pronuclear stage eggs. Data are needed to counsel patients about their individual benefits from this procedure. All fresh embryo transfer cycles performed from January 1994 until December 1998 in which supernumerary pronucleate eggs were cryopreserved (n = 557) were analysed retrospectively, together with data from all subsequent cycles involving transfers of frozen-thawed pronucleate eggs (n = 420) from January 1994 until June 2001. The additional cumulative pregnancy rate per fresh cycle was 11.5%. This rate depended on the number of embryos per transfer, i.e. 1.9, 8.2 and 13.0% respectively when one, two or three embryos were transferred (P < 0.05). A strong correlation was found between the numbers of cryopreserved pronucleate eggs and pregnancy rates, of 9.3, 10.5 and 17.1% when 1-3, 4-6, or at least 7 pronucleate eggs were available respectively. Additional benefit in terms of this rate from cryopreservation for a patient with and without a pregnancy in the fresh embryo transfer cycles was 5.3 and 12.7% respectively. It is concluded that higher pregnancy rates in cycles involving cryopreserved eggs for patients who did not become pregnant in fresh transfer cycles reveals the disadvantage of the German Embryo Protection Law, which does not allow embryo selection. Therefore, cryopreservation of pronucleate eggs with a higher developmental potential is possible. The total pregnancy rate could be raised from 28.0 to 35.5% per fresh transfer cycle.