**Abstract**

Oocyte cryopreservation is one of the state-of-art technologies in human reproductive medicine, which brings opportunities for women to preserve their fertility. In the present study, we analyzed the efficiency and outcomes of 8 years' autologous egg cryopreservation: Frozen oocytes were warmed from 120 cycles and oocyte survival, fertilization, blastocyst development, clinical pregnancy, embryo implantation, live birth rates and birth weights were collected based on the patients' ages of <35, 35–37 and > 37 years old. The details of oocyte cryopreservation and the efficiency were further analyzed based on different patient categories. During the study period, 849 oocytes from 120 cycles were warmed. Oocyte survival, fertilization, and blastocyst development were not affected by women's ages at the time of cryopreservation. However, number of patients without blastocyst formation was significantly (P < 0.05) higher in patients >37 years old (31.2%) than that in patients <35 years old (13.1%). Higher live birth rates were observed in patients <35 (51.1%) and 35–37 (46.7%) years old than in patients >37 years old (28.6%) after fresh embryo transfer. Some patients did not have blastocysts mainly due to low fertilization by poor sperm or small number of oocytes warmed. These results indicate that the efficiency of oocyte cryopreservation, evaluated by live birth and embryo implantation rates is affected by women's age, number of oocytes warmed and sperm quality.

**Keywords:** Oocyte cryopreservation, Fertility preservation, Fresh embryo transfer, Frozen embryo transfer, Implantation

#### **1. Introduction**

Oocyte cryopreservation is one of the state-of-art technologies in human assisted reproductive technologies (ART), which provides opportunities for women to preserve their fertility. Recently, the demand for oocyte cryopreservation has increased significantly, especially in women who want to delay childbearing for medical or no medial indications [1–9].

It has been reported that survival, fertilization, embryo development and pregnancy rates of cryopreserved/warmed human oocytes are similar to those of fresh oocytes, especially in young women and oocyte donors [10, 11]. The rates

of chromosomal abnormalities (embryonic aneuploidies), birth defects, or developmental deficits in offspring born from cryopreserved oocyte in vitro fertilization (IVF) were similar with those from fresh oocyte IVF [12]. However, fewer blastocysts were observed when cryopreserved oocytes were used for IVF as compared with fresh oocytes in patients who used autologous oocytes [13]. Furthermore, large clinical data reported by the Society for Assisted Reproductive Technology (SART) in USA indicated that fresh donor oocytes produced significantly higher live birth rate than cryopreserved donor oocytes [14] and the equivalency between fresh and cryopreserved oocytes still need more data to support [15].

As a new technology in human IVF, oocyte cryopreservation is still a challenge for IVF laboratories as it adds more laboratory manipulations on oocytes including cryopreservation and warming. Furthermore, the optimal time for oocytes to be cryopreserved after retrieval and for oocytes to be inseminated after warming may be different between patients. Therefore, differences in laboratory protocols may make the efficiency different and a case-specific protocol may be necessary to obtain the best outcome. More information remains to be collected whether oocyte cryopreservation will be widely offered to healthy women at any age as an approach to preserve fertility and delay childbirth [16, 17].

More women would like to give birth in their late 30s [4, 18]. However, women's fertility dramatically declines when they reach their late 30s, and further declines in their early 40s [4]. This phenomenon increases the demand for women to preserve their fertility by oocyte cryopreservation before their fertility declines [4, 18]. Although fertility preservation could benefit women who have hematologic diseases, breast cancer, some pelvic cancers and systematic diseases requiring chemotherapy, radiotherapy or bone marrow transplantation [2, 3, 19, 20], most users of this technology are healthy women who want to postpone childbearing [2, 3, 7, 8, 17, 18, 21, 22].

On the other hand, oocyte cryopreservation is offered not only to women for fertility preservation [7, 8, 21–23], it has also been offered to donor banks [24, 25], IVF patients as a backup technology. For example, in cases where semen sample may not be available on oocyte retrieval day, no motile sperm found in a semen sample, or there are not enough motile sperm for insemination of all oocytes retrieved. Some patients may produce a high number of oocytes and do not want to inseminate all, and some patients may want a limited number of oocytes to be fertilized [23]. Therefore, oocyte cryopreservation is required under various situations. Accordingly, the analysis of efficiency of clinical outcomes with cryopreserved oocytes becomes difficult.

The efficiency of human oocyte cryopreservation has been widely studied in donor oocytes and most data were collected from fresh embryo transfer [10, 11, 14, 15]. However, as preimplantation genetic testing for aneuploidies (PGT-A) and other genetic testing are very common in human IVF, it is required that biopsied embryos for testing are cryopreserved for later frozen embryo transfer (FET). Although cryopreservation by vitrification of human embryos from fresh oocytes does not affect embryo implantation [26–28], there is still no published evidence to address whether cryopreservation of embryos from frozen/warmed oocytes disturb embryo implantation or these embryos have a similar implantation as fresh embryos. Therefore, in the present study, we compared fresh blastocyst transfer and frozen/warmed blastocyst transfer to examine whether double cryopreservation (both oocyte and blastocyst cryopreservation) has a similar efficiency as single cryopreservation (oocyte cryopreservation) based on women's ages at the time of oocyte cryopreservation.

*Efficiency of Autologous Egg Cryopreservation: Eight Years' Experiences and Clinical Outcomes DOI: http://dx.doi.org/10.5772/intechopen.98675*
