Single or Double Elective Embryos Transfer Associated to Preimplantation Genetic Test in in Vitro Fertilization Cycles

Infertility is an important public health problem, affecting between 8 and 12% of reproductive-age couples, and leading to a high prevalence of childless couples (Bergstrom, 1992; Ombelet and Campo, 2007). The demand for infertility treatment is increasing due to sociocultural factors such as delayed pregnancy, higher incidence of sexually transmitted diseases, obesity rates, and greater acceptance to the available treatments. Recent estimates have shown that more than 1.8 million assisted reproduction treatments (ART) were performed in 2010 and more than 6 million children born were conceived using ART (Dyer et al., 2016).

In vitro fertilization (IVF) techniques have improved performance and currently provide a live embryo transfer rate that is around 25%. However, the success of IVF techniques depends on maximum efficiency in each treatment step, from controlled ovarian stimulation to obtaining adequate numbers of good quality mature eggs, optimal embryo culture conditions, availability of embryos of good quality for transfer and an adequate endometrium for implantation. Changes in clinical and laboratory practices such as the transfer of embryos in the blastocyst stage, improvement of cryopreservation techniques, transfer of thawed embryos after endometrial preparation and single embryo transfer (SET), have been increasingly indicated for patients with good prognosis. At the same time, the use of SET and freezing of all embryos for later transfer of thawed embryos are the major paradigms of ART in recent years (Chambers et al., 2016).

Despite a variation among countries influenced by coverage of health plans, legislation, guides to medical societies, population and culture, in Europe, on average 20% of transfers are single, with up to 69% of cycles in Sweden. In the United States, elective SET is still low, around 10% among women up to 35 years of age (Maheshwari et al., 2011; Practice Committee of the Society for Assisted Reproductive and Practice Committee of the American Society for Reproductive Medicine, 2012). Despite recommendations and increased SET practice, multiple gestation rates in IVF techniques are still high in the overall mean, around 20-25%, as a result of resistance of using SET and maintaining the transfer of multiple embryos with the purpose of obtaining higher gestation rates (Naasan et al., 2012, Kupka et al., 2014, Ishihara et al., 2015). This resistance is due to the idea that transferring more than one embryo may increase the chance of gestation. However, this practice does not take in consideration the increase of maternal and perinatal complications due to multiple pregnancies (Min et al., 2010; Practice Committee of American Society for Reproductive, 2012). In addition, studies have shown that cumulative live birth rates after the transfer of two SET cycles are comparable with a single transfer of two embryos (Pandian et al., 2009; Chambers and Ledger, 2014).

Historically, it is known that among the total number of retrieved oocytes, only a limited amount of them carry the potential to generate full-term gestation. Thus, embryo selection is a crucial step for the success of IVF techniques and the efficiency of this process is related to the decrease in the number of embryos to be transferred, since once it is possible to select embryos with greater implantation potential, the transfer of fewer embryos becomes more feasible and effective. In the routine, the embryonic selection is based on morphological criteria and characteristics of embryo development in order to infer its implantation potential (Ebner et al., 2003).

After controlled ovarian stimulation, approximately 50% of the embryos present chromosomal alterations (Munne et al., 1995). Then, the embryonic genetic evaluation is becoming increasingly used for the selection of euploid embryos for transfer. Blastocyst biopsy associated with chromosomal screening has been shown to be highly predictive of blastocyst developmental potential (Scott et al., 2012), increasing the chances of implantation by selection of euploid blastocysts for transfer in fresh (Scott et al., 2013) and frozen-thawed cycles (Schoolcraft and Katz-Jaffe, 2013).