A new study, published online in Human Reproduction, provides reassuring evidence on the outcome of children born after embryos were frozen and stored, before being thawed and transferred to the womb . The results are good news as an increasing number of children, estimated to be 25% of assisted reproductive technology (ART) babies worldwide, are now born after freezing or vitrification (a process similar to freezing that prevents the formation of ice crystals).
The study, led by Dr Ulla-Britt Wennerholm, an obstetrician at the Institute for Clinical Sciences, Sahlgrenska Academy (Goteborg, Sweden), reviewed the evidence from 21 controlled studies that reported on prenatal or child outcomes after freezing or vitrification.
She found that embryos that had been frozen shortly after they started to divide (early stage cleavage embryos) had a better, or at least as good, obstetric outcome (measured as preterm birth and low birth weight) as children born from fresh cycles of IVF (in vitro fertilisation) or ICSI (intracytoplasmic sperm injection). There were comparable malformation rates between the fresh and frozen cycles. There were limited data available for freezing of blastocysts (embryos that have developed for about five days) and for vitrification of early cleavage stage embryos, blastocysts and eggs.
"Slow freezing of embryos has been used for 25 years and data concerning infant outcome seem reassuring with even higher birthweights and lower rates of preterm and low birthweights than children born after fresh IVF/ICSI. For the newly introduced technique of vitrification of blastocysts and oocytes, very limited data have been reported on obstetric and neonatal outcomes. This emphasises the urgent need for properly controlled follow-up studies of neonatal outcomes and a careful assessment of evidence currently available before these techniques are added to daily routines. In addition, long-term follow-up studies are needed for all cryopreservation techniques," concluded Dr Wennerholm.
The above story is based on materials provided by European Society for Human Reproduction and Embryology. Note: Materials may be edited for content and length.
- U.-B. Wennerholm, V. S๖derstr๖m-Anttila, C. Bergh, K. Aittomไki, J. Hazekamp, K.-G. Nygren, A. Selbing, and A. Loft. Children born after cryopreservation of embryos or oocytes: a systematic review of outcome data. Human Reproduction, 2009; DOI: 10.1093/humrep/dep125
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