The effectiveness of flow cytometric sorting of human sperm (MicroSort®) for influencing a child's sex.

BACKGROUND: Flow cytometric sorting can be used to separate sperm based on sex chromosome content. Differential fluorescence emitted by stained X- vs. Y-chromosome-bearing sperm enables sorting and collection of samples enriched in either X- or Y-bearing sperm for use to influence the likelihood that the offspring will be a particular sex. Herein we report the effectiveness of flow cytometric sorting of human sperm and its use in human ART procedures. METHODS: This prospective, observational cohort study of the series of subjects treated with flow cytometrically sorted human sperm was conducted at investigational sites at two private reproductive centers. After meeting inclusion criteria, married couples (n = 4993) enrolled to reduce the likelihood of sex-linked or sex-limited disease in future children (n = 383) or to balance the sex ratio of their children (n = 4610). Fresh or frozen-thawed semen was processed and recovered sperm were stained with Hoechst 33342 and sorted by flow cytometry (n = 7718) to increase the percentage of X-bearing sperm (n = 5635) or Y-bearing sperm (n = 2083) in the sorted specimen. Sorted sperm were used for IUI (n = 4448) and IVF/ICSI (n = 2957). Measures of effectiveness were the percentage of X- and Y-bearing sperm in sorted samples, determined by fluorescence in situ hybridization, sex of babies born, IVF/ICSI fertilization- and cleavage rates, and IUI, IVF/ICSI, FET pregnancy rates and miscarriage rates. RESULTS: Sorted specimens averaged 87.7 ± 5.0% X-bearing sperm after sorting for X and 74.3 ± 7.0% Y-bearing sperm after sorting for Y. Seventy-three percent of sorts were for girls. For babies born, 93.5% were females and 85.3% were males after sorting for X- and Y-bearing sperm, respectively. IUI, IVF/ICSI, and FET clinical pregnancy rates were 14.7%, 30.8%, and 32.1%, respectively; clinical miscarriage rates were 15.5%, 10.2%, and 12.7%. CONCLUSIONS: Flow cytometric sorting of human sperm shifted the X:Y sperm ratio. IUI, IVF/ICSI and FET outcomes were consistent with unimpaired sperm function. Results provide evidence supporting the effectiveness of flow cytometric sorting of human sperm for use as a preconception method of influencing a baby's sex. TRIAL REGISTRATION: NCT00865735 (ClinicalTrials.gov).

Scientific aspects of preconception gender selection.

Although numerous methods have been promoted as having an influence on the gender of offspring, most lack credible scientific evidence of effectiveness. Preconception gender selection has an important application in reducing the risk of having children with X-linked disease. A preconception, flow cytometric sperm sorting method of gender selection (MicroSort) is based upon the detection of differential fluorescence emitted by fluorescently stained X and Y chromosome-bearing spermatozoa. Ongoing clinical trial results illustrate the safety and efficacy of the method. Fluorescence in-situ hybridization (FISH) analysis of specimens pre- and post-sort show the 50:50 X:Y ratio in unsorted spermatozoa can be shifted to 90% X or 75% Y after sorting. Embryo gender and fetal/baby gender are consistent with post-sort FISH results. Intrauterine insemination (IUI) and IVF/ICSI (intracytoplasmic sperm injection) pregnancy rates are consistent with those reported in the assisted reproduction literature. Clinical loss rates are similar to those in the general population. The observed major congenital abnormality rate of 2.05% for babies born after using this sperm sorting method coincides with that occurring spontaneously. Current results indicate that the method is a safe and effective process and is a valuable tool for families wishing to balance the gender distribution of their children or to reduce the likelihood of having children with X-linked disease.