Comparison of the major malformation rate of children conceived from cryopreserved embryos and fresh embryos

Background Cryopreserved embryo transfer has become indispensable in reproductive technology. More and morechildren are conceived from frozen-thawed embryo transfer (FET). The risk of birth defects associated with frozen-thawedembryo transfer has been evaluated and conflict results are obtained. The aim of this study was to compare the rate ofmajor malformations in children conceived from cryopreserved embryos with that of children from fresh embryos.Methods A retrospective analysis was performed on children conceived from frozen-thawed embryos and freshembryos between January 2005 and December 2008 at the Reproduction Center of the Third Hospital, Peking University.The major malformation rates were compared between two groups for all children, as well as singletons or twins,separately. The frequencies of different subtypes of malformations classified according to different organ system werealso compared.Results Thirty-four of 3125 children from cryopreserved embryos had a major malformation. The malformation rate was1.09%, which was comparable to that for children after fresh embryos transfer (1.53%(55/3604), OR: 0.71, 95%C/;0.46-1.09). The malformation rate was also similar when the analysis was limited to children from cryopreservedembryos resulted from in vitro fertilization (IVF)(1.39%)and fresh IVF(1.3%). However, children from cryopreservedembryos resulted from intracytoplasmic sperm injections (ICSI) had much lower malformation rate than from freshICSI(0.63% vs.1.83%, OR: 0.34, 95% CI: 0.16-0.75). No difference was found in the incidence of major malformations insingletons from cryo ICSI (0.73%) and fresh ICSI(1.9%), or from cryo IVF(1.49%) and fresh IVF(1.67%). Similarmalformation rate was found in multiples from cryo ICSI(0.52%) and fresh ICSI(1.76%), or cryo IVF(1.30%) and freshIVF(0.90%). The distribution and risk of the subtype of malformations, such as cardiovascular, gastrointestinal, neuraltube, urogenital, musculoskeletal and facial abnormalities was not different between the cryo group and fresh group.Conclusions The major malformation rate is similar between fetuses/children conceived from cryopreserved embryosand those from fresh embryos. Large prospective and long-term follow-up studies are needed to get exact resultsconcerning the birth defects of the children born after cryopreserved embryos.