Flow cytometric sorting of human sperm: MicroSort® clinical trial update

This report provides a summary of MicroSort® efficacy in separation of X- from Y-chromosome bearing human sperm (XSort® and YSort®, respectively), clinical outcomes, and the sex of the resultant babies when sorted sperm were used for intrauterine insemination (IUI), in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI). Clinical trial participants were married couples seeking reduced X-linked genetic disorder risk or family balancing. Sperm were stained with Hoechst 33342, sorted by flow cytometry, then used or cryopreserved for subsequent use. Fluorescence in situ hybridization (FISH) analysis determined the post-sort enrichment (purity) for X- and Y-bearing sperm. Birth and pediatric records were evaluated for incidence of congenital malformations. Between June 1994 and January 2007, patients underwent 3629 IUI cycles, 1642 IVF/ICSI cycles with fresh embryo transfer (ET) and 99 frozen embryo transfer (FET) cycles after MicroSort®. Of 5871 total sorts, 74.9% were XSort® and 25.1% were YSort®. IVF/ICSI fertilization rate was 70.7% and 93.8% of 2PN embryos cleaved. The pregnancy rates for IUI, IVF/ICSI, and FET were 15.6, 32.0, and 33.3%, respectively, while miscarriage rates were 15.7, 14.3, and 33.3%, respectively. Post-sort purity averaged 87.9% (XSort®) and 73.4% (YSort®). A total of 1125 clinical pregnancies yielded 943 babies born and 167 ongoing pregnancies. For babies born, XSort® resulted in 92.0% females and YSort® yielded 81.5% males. Postnatal follow-up showed a 2.6% major congenital malformation rate, with no recurrent pattern or clustering of malformations. FISH results confirmed MicroSort® enrichment of X- and Y-bearing sperm populations that closely corresponded with the sex of the resultant child. Fertilization, cleavage, spontaneous abortion, and pregnancy rates as well as incidence of major congenital malformations were comparable to those in literature reports utilizing unsorted sperm.