Selective vitrification of euploid oocytes markedly improves survival, fertilization and pregnancy-generating potential

Abstract

Enthusiasm for oocyte cryopreservation has been limited by poor pregnancy rates per thawed metaphase II (MII) oocytes (<4%) and low implantation rates per embryos. The reasons relate to technical limitations in the freezing process, and the fact that <40% of oocytes are euploid and unable to produce 'competent' embryos. Comparative genomic hybridization was performed on the first polar body (PB-1) of 323 MII oocytes retrieved from 16 donors. Of these, 111 were euploid, and were vitrified. Seventy-five of 78 vitrified oocytes (96%) survived warming and were fertilized using intracytoplasmic sperm injection. Thirty-one (41%) subsequently developed into expanded blastocysts, of which no more than two were subsequently transferred per uterus to 16 out of 19 prospective embryo recipients. Twelve of 19 (63%) recipients produced 17 healthy babies (eight singletons, three twins, and one set of triplets) One twin pregnancy miscarried in the late first trimester The birth rate per transfer of a maximum of two blastocysts to 16 recipients was 75%. The implantation rate per vitrified euploid oocyte was 27%. This study showed a six-fold improvement in pregnancy rate per cryopreserved oocyte over previous reports and a marked improvement in implantation rate. If independently validated, this approach could open the door to commercial egg cryobanking, significantly expanding women's reproductive choices.

Genetic analysis of human embryos by metaphase comparative genomic hybridization (mCGH) improves efficiency of IVF by increasing embryo implantation rate and reducing multiple pregnancies and spontaneous miscarriages

“…Comparative genomic hybridization has also recently gained attention as a potential means to enhance the selection of embryos used for transfer in the IVF setting (2,3). We recently reported (4,5) on two separate studies where CGH was performed on first polar bodies (PB1) to identify euploid oocytes. In the first study, chromosomal euploidy of PB1 DNA from metaphase II (MII) oocytes was the primary determinant of embryo competence.…”

“…In the second study, we selectively vitrified and cryobanked euploid (CGH-normal) oocytes (5). The subsequent transfer of %2 blastocysts derived from such warmed oocytes resulted in a 61% IR per blastocyst, a 75% BR following blastocyst transfer, and a 26% birth rate per warmed oocyte (5).…”

“…Fluorescence in situ hybridization (FISH) to diagnose oocyte/embryo aneuploidies is limited by the fact that at best it can only examine 12 chromosome pairs. Comparative genomic hybridization, on the other hand, evaluates all chromosomal gains and losses in a single hybridization of DNA samples (4,5) and can detect aneuploidies that would otherwise have been missed by FISH (6).…”

Application of intra- and extracellular sugars and dimethylsulfoxide to human oocyte cryopreservation

“…Earlier studies using mouse oocytes and zygotes also showed that microinjected trehalose at its effective concentrations was non-toxic and quickly eliminated during embryonic development [15,29]. In recent years, several studies reported excellent survival rates after vitrification of human oocytes [6,9,[32][33][34]. These results are encouraging; yet the vitrification procedure used in these studies requires direct contact with LN2, and thus is of concern due to contamination risk.…”

Effect of vitrification procedure on chromosomal status of embryos achieved from vitrified and fresh oocytes

“…Since the first pregnancy achieved with a vitrified/warmed human oocyte [83] and the first birth of a healthy baby [84], vitrification results have improved significantly during the last decade [17][18][19][20][21][22][23][24][25][26][85][86][87][88]. Vitrification is the glass-like solidification of a solution at low temperature, without ice crystal formation.…”