Clinical experience with preimplantation diagnosis of sex by dual fluorescent in situ hybridization

Purpose Our purpose was to assess the clinical application of dual fluorescent in situhybridization (FISH) for the diagnosis of sex in the human preimplantation embryo. Results Over a 2-year period, 18 couples at risk of transmitting X-linked recessive disorders underwent preimplantation diagnosis of embryo sex by dual FISH with X and Y chromosome-specific DNA probes. A total of 27 in vitro fertilization (IVF) treatment cycles led to nine pregnancies; 7 reached the stage of clinical recognition, of which 2 spontaneously aborted. There were five live births, three singleton and two twin: none in disagreement with the diagnosed sex. The diagnosis was corroborated in 51 of the 74 nontransferred embryos. The efficiency of the procedure improved throughout the four treatment cycles. This was reflected in the increased proportion of double embryo transfers (from 50% in series 1 and 2 to 100% in series 3 and 4), with a consequent improvement in pregnancy rate (from 28 to 71% per embryo transfer). The excess of male embryos (male∶female, 60∶40 overall) and the high proportion of biopsied embryos with abnormal numbers of X and Y chromosome signals (14.5%) effectively reduced the number of normal female embryos available for transfer. Conclusion Dual FISH is an efficient technique for determination of the sex of human preimplantation embryos and the additional ability to detect abnormal chromosome copy numbers, which is not possible via the polymerase chain reaction, (PCR), makes FISH the preferred technique.