Perinatal Outcomes in Pregnancies With a Low Fetal Fraction on Non Invasive Prenatal Testing [4N

Abstract

INTRODUCTION: Placental-origin cell-free maternal DNA is known as the fetal fraction (FF). Low FF is a risk factor for aneuploidy, and may be a risk factor for poor perinatal outcome. Our objective was to evaluate the relation between low FF, and perinatal outcome. METHODS: This is a retrospective review of singleton pregnancies who had NIPT. We compared the maternal BMI, gestational age of delivery (GA), birth weight (BW), and composite perinatal morbidity (CPM) between patients with a FF < 4% on NIPT (LFF), and those with a normal FF on their NIPT (NFF). The CPM was defined as the presence of any of the following complications: spontaneous abortion, hypertensive disorders of pregnancy, abruption, IUFD, preterm birth, low BW, NICU admission, or neonatal death. RESULTS: 256 patients were included. 28 (10.9%) had LFF, while 228 (89.1%) had NFF. Median age was 35-years, and median GA was 39 weeks. The rate of CPM in the entire cohort was 26.5%. Median BMI was significantly higher in the LFF group (27.4 vs. 22.1 kg/m2; p< .001). There were no significant differences in CPM, gestational age at delivery or BW. Among the 28 patients in the LFF group, median FF in cases with CPM was significantly lower than in cases without CPM (2.0% vs. 3.2%; p=.04). CONCLUSION: There were no significant differences in obstetric outcomes between the two groups. Within the LFF group, lower FFs were associated with a higher rate of CPM. Larger studies are necessary to evaluate the association between uncommon outcomes and FF.