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Recording available 2/16-5/2
Recording available 2/16-5/2
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Abstract Award
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Poster Session 4

Category: Clinical Obstetrics

Poster Session 4

(1017) Low fetal fraction and obstetric outcomes: Insights from a matched cohort study

Thursday, February 12, 2026
3:30 PM - 5:00 PM  

    Submitting Author and Presenting Author(s)

  • Alison Asirwatham, MD

    Fellow
    UMass Chan Medical School
    Worcester, Massachusetts, United States

    • Coauthor(s)

  • SZ

    Sabrina Zhang

    UMass Chan Medical School
    Worcester, Massachusetts, United States

  • LB

    Lauryn Bates

    UMass Chan Medical School
    Worcester, Massachusetts, United States

  • AZ

    Aspen Zheng

    UMass Chan Medical School
    Worcester, Massachusetts, United States

  • KL

    Katherine Leung, MPH

    Biostatistician
    UMass Chan Medical School
    Worcester, Massachusetts, United States

  • Heidi K. Leftwich, DO

    Associate Professor of Obstetrics and Gynecology
    UMass Chan Medical School
    Worcester, Massachusetts, United States

Objective:
Noninvasive prenatal screening analyzes cell-free DNA (cfDNA) from maternal plasma to detect fetal aneuploidy. Adequate fetal cfDNA is required and low fetal fraction (LFF) can lead to assay failure. LFF is seen with maternal obesity and aneuploidy but may reflect placental dysfunction. While prior studies have associated LFF with hypertension and other adverse outcomes, few have focused specifically on assay failures. We compared obstetric outcomes and placental pathology in patients with normal vs LFF and explored whether prenatal aspirin use is related to placentally mediated adverse outcomes in cases of LFF.

Study Design:
Retrospective 1:3 matched cohort study of pregnancies at our center (2018-2023) with cfDNA performed ≥ 10 weeks’ gestation and 1st trimester ultrasound or reliable menstrual dating. Cases were defined as a “no call” cfDNA result due to low fetal fraction (< 4%), matched to controls by age, parity, and BMI. Exclusions included fetal anomaly, aneuploidy, multifetal gestation, and prenatal anticoagulant use. We compared perinatal outcomes and placental pathology between groups and examined outcomes in cases between aspirin use.

Results:

118 cases and 354 controls included. Baseline characteristics were similar, though LFF had fewer male fetuses and were more likely to have a history of hypertension in a prior pregnancy. Those in the LFF group tended to deliver earlier (OR 0.89, p=0.045) and had increased odds of preeclampsia without severe features (OR 2.47, p=0.041). No other differences in outcomes or placental pathology were seen, though a trend towards increased odds of decidual vasculopathy in the LFF group (OR 2.87, p=0.055) was noted. Aspirin use was not related to outcomes in the LFF group.

Conclusion:

After matching, LFF was associated with earlier delivery and higher odds of preeclampsia, supporting its role as a potential marker of placental dysfunction. A trend towards increased decidual vasculopathy reinforces this association. Aspirin use was not associated with a difference in outcomes, highlighting the need for further study of targeted interventions.