Preimplantation Genetic Diagnosis of Structural Abnormalities

Preimplantation genetic diagnosis (PGD) of translocations can be achieved through a variety of methods. For female carriers, a possibility is by polar body biopsy and analysis of its metaphase chromosomes using painting probes. For male carriers or female carriers with terminal breakpoints, metaphase chromosomes can also be studied by fusing blastomeres to enucleated oocytes. Otherwise, interphase analysis of the translocation can be performed using distal, subtelomeric or breakpoint spanning probes. The results obtained after PGD of translocations indicate a significant decrease in spontaneous abortions after the procedure, a good selection against unbalanced oocytes and embryos, and pregnancy rates that depend on the type of translocation involved. Balanced translocations occur in 0.2% of the neonatal population, but at a higher rate among infertile couples and patients with recurrent abortions. In a recent report, balanced translocations were found in 0.6% of infertile couples, 3.2% of couples that failed over ten IVF cycles, and 9.2% among fertile couples experiencing three or more consecutive first-trimester abortions (Hum. Reprod. 14 (1999) 2097). They were also found in 2-3.2% of males requiring ICSI (Hum. Reprod. 11 (1996) 2609; Hum. Reprod. 13 (1998) 576). PGD can be offered to carriers of balanced translocations as an alternative to prenatal diagnosis and pregnancy termination of unbalanced fetuses. In recent years, PGD for structural chromosome abnormalities has been attempted by a variety of approaches. The aims of PGD for translocations are to reduce the rate of spontaneous abortions that this population suffers and to minimize the risk of conceiving an unbalanced baby.