EMBRYO FREEZING - IS IT SAFE

The evidence for the safety of human embryo cryopreservation is review ed, Overall there is little to cause concern, Freezing is lethal for s ome embryos and it is unclear whether the survivors retain their full viability, Nevertheless, the rates of pregnancy and live births per co llection cycle are increased when surplus embryos are cryopreserved, T here is no increase in obstetric and perinatal complications in pregna ncies resulting from the transfer of frozen embryos, The incidence of birth defects is not affected by freezing and the development of child ren conceived from cryopreserved embryos appears normal, In the majori ty of studies on animal embryos no detrimental effects of freezing wer e identified. There is one report of subtle morphological, development al and behavioural changes in a long-term study of mice conceived from frozen embryos, but this remains to be substantiated, Pregnancies con ceived from frozen embryos should be followed and the occurrence of bi rth defects recorded. The ethics of the long-term follow-up of childre n is questioned. Emphasis should be placed on increasing the survival of embryos after freezing.