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CME Credit Offered
CME Credit Offered
Abstract Award
Abstract Award
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Poster Session 1

(245) Establishing the most accurate due date in twin gestation by second and third trimester ultrasound

Thursday, January 30, 2025
10:30 AM – 12:30 PM  

    Submitting Author and Presenting Author(s)

  • Katelyn J. Rittenhouse, MD

    Global Women's Health Fellow
    University of North Carolina - Chapel Hill
    Chapel Hill, North Carolina, United States

    • Coauthor(s)

  • AV

    Ambika V. Viswanathan, MD (she/her/hers)

    Medical Student, Department of Obstetrics & Gynecology
    University of North Carolina at Chapel Hill
    Chapel Hill, North Carolina, United States

  • TP

    Teeranan Pokaprakarn, PhD

    Research Assistant Professor
    University of North Carolina at Chapel Hill
    Chapel Hill, North Carolina, United States

  • YS

    Yuri Sebastião, PhD

    Research Assistant Professor
    University of North Carolina at Chapel Hill
    Chapel Hill, North Carolina, United States

  • Elizabeth M. Stringer, MD, MSc

    Professor of Maternal Fetal Medicine
    University of North Carolina at Chapel Hill
    Chapel Hill, North Carolina, United States

  • William H. Goodnight, MD (he/him/his)

    Associate Professor of Maternal Fetal Medicine
    University of North Carolina at Chapel Hill
    Chapel Hill, North Carolina, United States

  • JS

    Jeffrey S.A. Stringer, MD

    Professor of Obstetrics & Gynecology
    University of North Carolina at Chapel Hill
    Chapel Hill, North Carolina, United States

Objective: We assessed the optimal sonographic dating approach for twin gestations presenting to antenatal care beyond the first trimester.

Study Design:

We studied twin pregnancies receiving care at the University of North Carolina between Nov 2017 and Aug 2023 whose gestational age (GA) had been definitively established by first trimester ultrasound or in vitro fertilization (“ground truth”). We included all ultrasound studies with complete biometry conducted after 14 weeks gestation. We assessed the accuracy of Hadlock IV GA dating using the smaller, average, and larger twin’s biometric data against “ground truth” gestational age.

Results:

Our analysis dataset consisted of 2,103 studies from 593 twin pregnancies. 27% (161) pregnancies were monochorionic and 1% (8) were monoamniotic.  The mean absolute error ± standard error (MAE ± SE) was 5.77 ± 0.12 days for the smaller twin, 4.41 ± 0.09 days for the average twin, and 4.06 ± 0.07 days for the larger twin. The average error (AE) showed that all three measurements underestimated gestational age when compared to ground truth, with the larger twin having the least bias (smaller twin -4.53 ± 0.14; average twin -2.28 ± 0.12; larger twin -0.03 ± 0.12). These results held across sensitivity analyses including only one ultrasound scan per pregnancy and stratifying by chorionicity.

Conclusion:

In the 2nd and 3rd trimesters, gestational age dating is more accurate and less biased when using the biometry of the larger twin, as compared to the smaller twin or an average of the two twins. Guidelines should be updated to provide clear guidance on establishing twin GA when the dating ultrasound is performed beyond the first trimester.