Live birth from oocytes cryopreserved with slow-freezing protocol and thawed after 6 years of storage

After the birth of more than 900 babies from human cryopreserved oocytes with no apparent increase in congenital anomalies compared to conventional IVF babies [1], oocyte cryopreservation has become a quite widespread technique in Assisted Reproductive Technologies (ART), even in the female fertility preservation programs. Today two procedures are available for oocyte cryopreservation: slow-freezing (SF), the first protocol introduced, and vitrification (VT) [2]. The main goal of VT is to achieve high cryoprotectant concentration in order to increase the viscosity of the cryoprotectant solution and to suppress ice nucleation [3]. Biological and clinical outcomes of SF protocols seem to be less than those obtained with fresh and vitrified oocytes [4–6]. Oocyte cryopreservation is usually used in ART laboratories for supernumerary oocyte storage after Controlled Ovarian Stimulation (COS) [4], prevention of Ovarian HyperStimulation Syndrome (OHSS) risk, oocyte accumulation in poor responder patients [7], and fertility preservation programmes for cancer patients [8–10] or for social reasons [11]. Nevertheless, in 2008 the Practice Committee of American Society of Reproductive Medicine (ASRM) concluded that “Oocyte cryopreservation presently should be considered an experimental technique,” as the data available on the efficacy of oocyte cryopreservation in relation to the length of storage are still limited [1,12]. Instead, the ASRM considers embryo cryopreservation a non-experimental technique [12], with a proven clinical outcome regardless of the length of storage [13,14]. Unfortunately, there are limited data concerning children born from long-term cryopreserved oocytes [1]. The first live birth obtained from oocytes stored for a long period was reported by Yang et al. in 2007: oocytes were cryopreserved by SF for fertility preservation before cancer treatment and thawed 6 years later . In 2008, Parmegiani et al. reported a live birth from oocytes cryopreserved by SF after 5 years of storage in a patient who underwent infertility treatment. Kim and Hong [17] recently described a similar result, reporting a live baby born from vitrified oocytes thawed 5 years later . Here we describe the case of a woman who underwent ART procedures for both female (tubal) and male (oligoastenotheratozoospermia) infertility in our non private sterility center. The patient gave birth to two babies in two different thawing cycles from cryopreserved oocytes with SF protocol: the first baby after 11 months and the second baby after 6 years of storage.