First successful pregnancy in Switzerland after prospective sex determination of the embryo through the separation of X-chromosome bearing spermatozoa.

Question Under Study: The feasibility and the potential advantages of separating X-chromosome bearing spermatozoa for the prevention of a severe X-chromosome linked disorder with the use of intracytoplasmic sperm injection are presented.

Method: A carrier of muscular dystrophy type Becker was treated with intracytoplasmic sperm injection, using spermatozoa previously stained with the Hoechst dye 33342 and sorted with flow cytometry.

Results: After transfer of one single blastocyst, an intrauterine pregnancy arose. In the ninth week of gestation, the female sex of the embryo was confirmed with proof of absence of the SRY gene of the Y-chromosome. After normal pregnancy, the patient delivered a healthy daughter.

Conclusions: The staining of spermatozoa with specific markers and sorting with flow cytometry provides a means of preventing significant disease in the offspring and may help in reducing the number of surplus embryos needed for preimplantation genetic diagnosis.