Unexpected gender bias found in IVF cycles for sex selection

Abstract

Although regional biases towards selection of XX embryos using PGD is well described, gender preferences in the United States have not been assessed. Couples using PGD for elective sex selection must determine the disposition of supernumerary embryos of the undesired sex. We set out to describe clinical outcomes and elucidate patterns of sex selection PGD cases, so patients can be appropriately counseled by their physicians. Retrospective data analysis. Records of consecutive IVF-PGD cases for sex selection from July 2003 – December 2006 were reviewed. FISH analysis of chromosomes 13, 18, 21, X and Y was performed on single biopsied blastomeres. Statistical analysis was performed using chi-square test. Of 30 PGD cases, 4 were to avoid X-linked disease and 26 for elective sex selection; of which sixteen (61.5%) were performed to identify and select XX embryos and 10 for XY embryos. Overall, 54.8% (103/188) of the embryos were XY and 52.7% (99/188) were euploid for the chromosomes analyzed. The distribution of aneuploid embryos was similar between XX and XY embryos. Embryos of the desired sex were transferred in 67% of cases. Eight patients (26.6%) did not have an ET because all embryos were of the undesired sex (5/30), all were aneuploid (2/30) or all arrested in culture (1/30). Two patients opted to transfer embryos of the alternate sex and had a mixed transfer (9.1%). Of the 20 cycles that had an ET of the desired sex, 7 (35%) had only a single embryo available to transfer. The clinical pregnancy rate of patients who had an ET of only the desired sex was 45% (9/20) and the implantation rate was 35%. Euploid embryos of the undesired sex were available in 60% of cases, however only 50% of the couples chose to freeze these embryos. Bias against XX embryos was not observed in our small sample in contrast to world-wide trends. XX embryos were desired 2:1 over XY embryos. Only 2/3 of couples undergoing this procedure for elective sex selection underwent an ET of the desired sex. Although acceptable clinical pregnancy and implantation rates were achieved, the reduced number of available euploid embryos of the desired sex limits potential success rates. The choice made by couples with embryos that were genetically normal, but of the undesired sex, demonstrated that 50% of couples do not discard these embryos. This finding, along with the 2 couples that accepted mixed sex transfers, demonstrates that the initial desire for only one sex is not an absolute.