Clinical aspects and perinatal outcomes after cryopreservation of embryos and gametes

Cryopreservation techniques play today a central role in assisted reproduction, as they enhance the overall efficacy of in vitro fertilization (IVF) treatments by allowing the banking of supernumerary embryos obtained in these treatments, and their later use. The transfer of frozen/thawed embryos was established nearly 30 years ago, and although it has been clinical routine for a long time, the importance of freezing embryos has been newly emphasized. As recognized downsides of IVF treatment include the high prevalence of perinatal complications due to multiple births, the recommended practice of transferring fewer embryos in the fresh IVF treatment cycle, with the goal of performing single embryo transfer and the cryostorage of remaining embryos for their later use in frozen-thawed cycles, one at a time, is currently the trend. Also of great importance, cryopreservation techniques for spermatozoa and oocytes have additionally permitted gamete storage for long-term and the implementation of several new treatment modalities for assisted reproduction. Most of these methods are applied today in clinical programs of fertility preservation and third-part reproduction, such as sperm- and egg donor programs. Use of frozen thawed sperm has been in clinical use for over 50 years and banking sperm has been routinely offered to men, usually before gonadotoxic treatments, but also in many cases, practised as a "safety policy" previously to a vasectomy. Freezing methods for women's egg have required a much longer time to achieve a comparable effective clinical standard. Only recently, with the development of vitrification of oocytes, the clinical standard was recognized and since 2013 when the label "experimental" was removed, the freezing of oocytes could be regarded as an established method, and its use extended into clinical practice for fertility preservation but also performed after personal requirements, so called, "social freezing".