Embryo development of fresh 'versus' vitrified metaphase II oocytes after ICSI: a prospective randomized sibling-oocyte study

Abstract

BACKGROUNDA successful oocyte cryopreservation programme is of utmost importance where a limited number of oocytes can be inseminated per cycle, to overcome legal and ethical issues related to embryo storage, for oocyte donation programmes and for fertility preservation (especially for cancer patients). Vitrification has been recently proposed as an effective procedure for this purpose.METHODSIn order to validate the effectiveness of oocyte vitrification a non-inferiority trial was started on sibling metaphase II (MII) oocytes. To demonstrate the non-inferiority based on an absolute difference of 17% in the fertilization rate per sibling oocyte, a minimum of 222 oocytes were required. After oocyte denudation, MII oocytes with normal morphology were randomly allocated to fresh ICSI insemination or to vitrification procedure. If pregnancy was not obtained a subsequent ICSI cycle was performed with warmed oocytes of the same cohort. In both groups, three oocytes were inseminated per cycle by ICSI procedure. Primary end-points were fertilization rates calculated per warmed and per injected oocytes. Secondary end-points were zygote and embryo morphology.RESULTSA total of 244 oocytes were involved in this study. Of the 120 fresh sibling oocytes inseminated, 100 were fertilized (83.3%). Survival rate of sibling vitrified oocytes was 96.8% (120/124 oocytes). Fertilization rate after ICSI was 76.6% (95/124) per warmed oocyte and 79.2% (95/120) per survived/inseminated oocyte. No statistical difference in fertilization rates was observed between the two groups when calculated per sibling oocytes (absolute difference −6.73%; OR: 0.65; 95% CI = 0.33–1.29; P = 0.20) and per inseminated oocyte (absolute difference −4.17%; OR: 0.76; 95% CI = 0.37–1.53; P = 0.50). Embryo development was also similar in both treatment groups up till Day 2. The percentage of excellent quality embryos was 52.0% (52/100) in the fresh group and 51.6% (49/95) in the vitrification group (absolute difference −0.43%; OR: 0.98; 95% CI = 0.53–1.79; P = 0.9). The mean age of the 40 patients included in this study was 35.5 ± 4.8 years (range 26–42). Fifteen clinical pregnancies were obtained in the vitrification cycles of 39 embryo transfers performed (37.5% per cycle, 38.5% per embryo transfer), with an implantation rate of 20.2% (19/94). Three spontaneous miscarriages occurred (20%). Twelve pregnancies are ongoing (30.0% per cycle, 30.8% per embryo transfer) beyond 12 weeks of gestation.CONCLUSIONSOur results indicate that oocyte vitrification procedure followed by ICSI is not inferior to fresh insemination procedure, with regard to fertilization and embryo developmental rates. Moreover, ongoing clinical pregnancy is compatible with this procedure, even with a restricted number of oocytes available for insemination. The promising clinical results obtained, in a population of infertile patients, need to be confirmed on a larger scale.Clinical Trials Registration number: iSRCTN60158641.

Morphokinetics analysis of embryos derived from vitrified/warmed oocytes

“…Overall, present data assessing morphology and development of VODE and FODE do not show any major difference between the two groups. Our results are reassuring, and they are in line with published data showing that vitrification/warming cycles do not alter oocyte quality or resulting embryo development [6,11].…”

“…Overall, results obtained in the present investigation confirmed previous studies demonstrating the safety and the efficiency of opened system based vitrification techniques (oocytes are directly in contact with liquid nitrogen during vitrification) [1][2][3][4][5][6][7][8]13]. Since closed system based vitrification techniques are mostly used in France, it is worth testing these Fig.…”

“…Oocyte vitrification is widely used in assisted reproductive technology (ART) laboratories for several indications like diminution of frozen embryo number and egg banking for donation to fertility preservation [1][2][3][4][5][6][7][8]. To date vitrification is the most attractive and reliable option to store oocytes, bringing about a dramatic change in the field of ART [9,10].…”

“…To date vitrification is the most attractive and reliable option to store oocytes, bringing about a dramatic change in the field of ART [9,10]. Although this technique was shown to have no major adverse effect on oocyte ultrastructure and oocyte in vitro performance [6,11], it was suggested to indirectly impact on derived embryo development [12]. To date, vitrified/ warmed oocyte-derived embryo kinetics and morphology have not yet been entirely documented.…”

Live birth after 6 years of oocyte vitrification in a survivor with breast cancer

“…Cryopreservation of mature oocytes using vitrification techniques to avoid ice crystal formation has become an effective method to store oocytes, which supports it usefulness for fertility preservation. The technique achieves pregnancy rates close to those of current IVF with fresh oocytes and no apparent increase in congenital abnormalities [11][12][13][14][15].…”