Sex chromosome aneuploidy screening in a general population.

Cell-free fetal DNA testing is being used in parallel or in contingency screening as part of the first trimester screen. The test has high sensitivity and specificity for the trisomies 21, 18 and 13. The test also offers the option of assessing sex chromosome aneuploidies (SCA) which are recognised to be the next most common group of aneuploidies in the live birth population. Companies that offer the sex chromosome assessment report an accuracy rate of above 99% and a significant number of high-risk results have been detected in a multi-site Australian ultrasound practice. A high proportion of these women underwent prenatal testing to further assess the sex chromosomes. This study reports the results of these invasive investigations and results show that many of the high-risk SCA results appear to be false positives. This study reports the clinical experience of cell-free fetal DNA (cfDNA) testing with regard to sex chromosome aneuploidies in singleton pregnancies for a multi-site Sydney specialist O&G Ultrasound practice.