The association of HBB-related significant hemoglobinopathies and low fetal fraction on noninvasive prenatal screening for fetal aneuploidy

Objectives: HBB-related significant hemoglobinopathies have been anecdotally associated with low fetal fraction on noninvasive prenatal screening (NIPS). We sought to compare the difference in fetal fraction using NIPS in women with HBB-related significant hemoglobinopathies (HSH) and women with normal hemoglobin. Study design: This is a retrospective case-control study. Cases were women with a diagnosis of HSH using NIPS from a commercial laboratory. The comparison group was women with hemoglobin AA from a tertiary care center database. We tested for differences in median fetal fraction using quantile regression analysis, adjusting for maternal body weight and gestational age. Results: This study includes 35 women with clinically significant HSH and a comparison group of 636 women with hemoglobin AA. Adjusting for gestational age and body weight, the median fetal fraction was 4.1 point lower in the HSH than in the comparison group (beta - 4.1; 95% -5.7 to -2.5, p < .05). The rate of no-calls due to low fetal fraction was significantly higher in the clinically significant HSH group than in the comparison group [HSH: n = 9/35, 25.7% versus comparison: n = 32/636, 5.0% (p < .001)]. Conclusion: Women with HSH were more likely to have a lower fetal fraction and ultimately a five-fold higher no-call rate. What's already known about this topic? Low fetal fraction is one of the most common causes of no-call result in noninvasive prenatal screening High maternal weight, early gestational age and fetal aneuploidies are associated with low fetal fraction What does this study add? HBB-related significant hemoglobinopathies are associated with low fetal fraction Reduction in fetal fraction due to HBB-related significant hemoglobinopathies may also result in higher no-call rate