Conversion and non-conversion approach to preimplantation diagnosis for chromosomal rearrangements in 475 cycles.

Due to the limitations of preimplantation genetic diagnosis (PGD) for chromosomal rearrangements by interphase fluorescent in-situ hybridization (FISH) analysis, a method for obtaining chromosomes from single blastomeres was introduced by their fusion with enucleated or intact mouse zygotes, followed by FISH analysis of the resulting heterokaryons. Although this allowed a significant improvement in the accuracy of testing of both maternally and paternally derived translocations, it is still labour intensive and requires the availability of fertilized mouse oocytes, also creating ethical issues related to the formation of interspecies heterokaryons. This method was modified with a chemical conversion procedure that has now been clinically applied for the first time on 877 embryos from PGD cycles for chromosomal rearrangements and has become the method of choice for performing PGD for structural rearrangements. This is presented within the context of overall experience of 475 PGD cycles for translocations with pre-selection and transfer of balanced or normal embryos in 342 (72%) of these cycles, which resulted in 131 clinical pregnancies (38%), with healthy deliveries of 113 unaffected children. The spontaneous abortion rate in these cycles was as low as 17%, which confirms an almost five-fold reduction of spontaneous abortion rate following PGD for chromosomal rearrangements.

Chromosomal abnormalities in a series of 6,733 human oocytes in preimplantation diagnosis for age-related aneuploidies.

Most chromosomal abnormalities originate from female meiosis and contribute significantly to pregnancy failures, particularly in women of advanced maternal age. A total of 8,382 oocytes were obtained in 1,297 IVF cycles from patients of advanced maternal age (mean 38.5 years). Following a standard IVF protocol, oocytes were tested following removal and fluorescence in-situ hybridization (FISH) analysis of the first (PB1) and second polar bodies (PB2), using probes specific for chromosomes 13, 16, 18, 21 and 22 (Vysis). FISH results were available in 67,33 (80.3%) oocytes tested, 3,509 (52.1%) of which were aneuploid, with the remaining 3,224 (47.9%) normal oocytes available for transfer. In all, 41.7% of oocytes had meiosis I errors, compared to 35.1% with meiosis II errors. Abnormalities in meiosis I were represented by extra chromatids in 15.4%, missing chromatids in 48.1%, missing chromosomes in 5.9%, extra chromosomes in 0.5%, and complex abnormalities in 30.1%. The proportions of abnormal oocytes with missing or extra chromatids in meiosis II were 36.6 and 41.2% respectively, with the remaining oocytes having complex abnormalities, involving missing or extra chromatids of different chromosomes (22.1%) following meiosis II. Overall, 41.8% oocytes had meiosis I, 30.7% meiosis II, and 27.6% both meiotic division errors. A total of 45.1% of the abnormal oocytes had complex errors, involving the same chromosome in both meiotic divisions (21.5%), or different chromosomes (78.5%), of which 74.8% were with abnormalities of two, and 25.2% with abnormalities of three chromosomes studied. Of 3,224 detected aneuploidy-free zygotes, 2,587 were transferred in 1,100 treatment cycles (2.35 embryos per transfer), resulting in 241 (21.9%) clinical pregnancies and 176 healthy children born, suggesting a positive clinical outcome following aneuploidy testing of oocytes in a group of IVF patients of average age 38.5 years.