a1 Center for Reproductive Medicine and Infertility, New York Hospital-Cornell University Center, New York, Division of Molecular Cytometry, University of California, San Francisco, and Department of Life Sciences, Lawrence Berkeley Laboratory, Berkeley, California, USA.
Evidence of sexual dimorphism before fetal gonadal differentiation in mammals has been accumulating, suggesting that male embryos develop faster than female ones. The current investigation was performed to evaluate whether the development rate of precompacted human embryos is controlled by sex chromosomes. Sex was determined by polymerase chain reaction and fluorescence in situ hybridisation in 172 arrested embryos derived from in vitro fertilisation. The sex ratio (1.02:0.98) did not differ significantly from 1:1. Although more males appeared to have greater fragmentation, the difference between the sex ratios of highly fragmented and normal embryos (1.08:0.92) was not significant. Arrested female embryos had a tendency to exhibit more than five nuclei and less than 10% fragmentation, but the trend was not statistically significant. The current results suggest that the first developmental block in human embryos occurs prior to and shortly after genomic activation and is not determined by the presence of the Y chromosome.
c1 S. Munné, Gamete and Embryo Research Laboratory, Cornell University Medical College, PO Box 30, 1300 York Avenue, New York, NY 10021, USA.
1 Gamete and Embryo Research Laboratory, Center for Reproductive Medicine and Infertility, Department of Obstetrics and Gynecology, New York Hospital-Cornell University Medical Center, New York, NY 10021, USA.
2 Division of Molecular Cytomerry MCB 230, Department of Laboratory Medicine, University of California, San Francisco, Ca 94143–0808, and Department of Life Sciences, Lawrence Berkeley Laboratory, Berkeley, CA 904720, USA.