Births resulting from oocyte cryopreservation using a slow freezing protocol with propanediol and sucrose

The human mature oocyte is particularly sensitive to cooling and low temperatures in addition to freeze-thaw damage. The efficiency of oocyte cryopreservation including the pregnancy outcome is still low. The aim of our study is to briefly introduce our preliminary clinical results achieved with oocyte cryopreservation (CP). Our work focused on the use of a slow cooling procedure using the cryoprotectants propanediol (1.5 M) and sucrose (0.3 M). Following a short incubation of 4-6 hours thawed oocytes were injected with a single sperm (ICSI) and fertilization was assessed 12-16 hours later. Laser assisted hatching (LAH) was performed on all transferred embryos and embryo transfer (ET) was carried out 48-72 hours after ICSI. One-hundred and ten eggs were thawed and a survival rate of 76% (84/110) was obtained. Of the 84 oocytes which survived, 64 subsequently fertilized (64/84; 76%) following ICSI and on the following day 55 of those had cleaved (55/64; 86%). Fifty-two embryos were transferred in 29 patients (1.8 embryo/patient), and 7 (7/29; 24%) resulted in clinical pregnancy (1 twin pregnancy). One of the pregnancies encountered first trimester abortion (1/7; 14%). Implantation rate of 15.4% per embryo transferred (8/52) and 7.3% per egg thawed (8/110) were obtained. In all cases, chorion biopsy was performed and chromosomal anomalities were not detected. Our results provide further evidence that the procedure can be applied safely and with good success in clinical assisted reproduction. However, more work is needed since the survival and implantation rate should be improved.