Single-nucleotide polymorphism microarray-based preimplantation genetic diagnosis is likely to improve the clinical outcome for translocation carriers

Study question: Is preimplantation genetic diagnosis (PGD) for translocation carriers more effective when done with a single-nucleotide polymorphism (SNP) array using trophectoderm (TE) biopsy and frozen embryo transfer (FET) compared with traditional PGD based on fluorescence in situ hybridization (FISH-PGD) using blastomere biopsy and fresh embryo transfer?

Summary answer: The procedure using the SNP array combined with TE biopsy and FET significantly improves the clinical pregnancy rate for translocation carriers. The miscarriage rate also slightly decreases.

What is known already: FISH-PGD has been widely used in translocation carriers but the clinical outcomes have not been ideal. SNP arrays can detect both chromosome segmental imbalances and aneuploidy, and may overcome the limitations of FISH in PGD for translocation carriers.

Study design, size and duration: This was a retrospective study of 575 couples with chromosomal translocations, including 169 couples treated by SNP-PGD between October 2011 and August 2012, and 406 couples treated by FISH-PGD between January 2005 and October 2011.

Participants/materials, setting, methods: The study was set in an IVF center at the Reproductive and Genetic Hospital of CITIC-Xiangya, China. In total, 169 couples underwent SNP analysis, including 52 Robertsonian translocation carriers and 117 carriers of reciprocal translocations. Blastocysts (n = 773) were biopsied and FET was carried out on the balanced embryos. Four hundred and six couples underwent FISH-PGD, including 149 Robertsonian translocation carriers and 257 reciprocal translocation carriers. In total, 3968 embryos were biopsied and balanced embryos were transferred fresh. The SNP-PGD results and clinical outcomes were compared with those of FISH-PGD.

Main results and the role of chance: Reliable SNP-PGD results were obtained for 717 out of 773 (92.8%) biopsied blastocysts. The proportions of normal/balanced embryos, embryos with translocation-related and translocation-unrelated abnormalities, the median number of embryos per patient, the ongoing pregnancy rate per embryo transfer and the miscarriage rate were 58, 23, 19, 2, 69 and 12%, respectively, for Robertsonian translocation carriers and 36, 52, 12, 1, 74 and 11%, respectively, in reciprocal translocation carriers. Reliable FISH-PGD results were obtained for 3452 out of 3968 (87.0%) biopsied embryos. The proportions of normal/balanced embryos, unbalanced embryos, the median number of embryos per patient, the ongoing pregnancy rate per transfer and the miscarriage were 36, 64, 3, 38 and 17%, respectively, for Robertsonian translocation carriers and 20, 80, 1, 39 and 16%, respectively, for reciprocal translocation carriers. Thus, SNP-PGD achieved a higher pregnancy rate but a lower miscarriage rate than FISH-PGD. There were no significant differences in maternal age, basal endocrine level and the average number of retrieved oocytes and good-quality D3 embryos in the SNP-PGD group compared with the FISH-PGD group.

Limitations, reasons for caution: This was a retrospective study with the two groups treated in different periods; therefore, there is a chance of sample bias and a possibility that the results were influenced by other factors that changed over time. Furthermore, the two treatment protocols differ in several respects and we cannot say which makes the greatest contribution to the difference in success. Complete pregnancy outcomes of SNP-PGD have not been obtained as some embryos have not been transferred yet. We cannot exclude differences between the final data and the data in the present manuscript.

Wider implications of the findings: The adoption of SNP-PGD combined with TE biopsy and FET may significantly improve the clinical pregnancy rate, and decrease the miscarriage rate after PGD for translocation carriers.