Low first-trimester fetal fraction is associated with chronic inflammation in the placenta

BACKGROUND: Some data suggest an association between abnormal fetal fraction on noninvasive prenatal screening and adverse pregnancy outcomes, including low birthweight, preeclampsia, and preterm birth in the absence of aneuploidy. These findings suggest that abnormal fetal fraction may be associated with placental pathologic processes in early gestation.OBJECTIVE: This study aimed to determine the independent associa-tion of fetal fraction on genetic noninvasive prenatal screening with histo-logic placental types.STUDY DESIGN: This was a retrospective cohort study at a single institution in the period between January 2017 and March 2021, including live births at =24 weeks for which noninvasive prenatal screening was performed and placental pathology results were available. Results were stratified by trimester of noninvasive prenatal screening. Clinical charac-teristics were compared by quartile of fetal fraction using chi-square tests. Linear regression was used to model continuous fetal fraction as a func-tion of 3 histologic types representing chronic placental injury-chronic inflammation, maternal vascular malperfusion, and fetal vascular malper-fusion. Inverse probability weighting was used to account for selection bias in characteristics of patients with placental pathology examination.RESULTS: A total of 1374 patients had noninvasive prenatal screening in the first trimester and 262 in the second trimester. Preterm birth and hypertensive disorders of pregnancy were most common in the lowest quartile of fetal fraction. Chronic inflammation was associated with a 0.56 percentage point reduction in fetal fraction (95% confidence interval,-0.95 to-0.16), and maternal vascular malperfusion was associated with a 0.48 percentage point reduction in fetal fraction (95% confidence interval,-0.91 to-0.04) in adjusted models. The association with mater-nal vascular malperfusion was no longer statistically significant after accounting for selection bias in placentas sent for pathologic examination. Second-trimester fetal fraction was not associated with placental pathology.CONCLUSION: Chronic inflammation is associated with lower first-tri-mester fetal fraction even after accounting for selection bias. Higher fetal fraction in the second trimester was associated with fetal vascular pathol-ogy, although this association was no longer statistically significant after inverse probability weighting to account for selection bias. First-trimester fetal fraction may be a biomarker of adverse outcomes associated with chronic inflammation.