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Clinical Obstetrics

Poster Session 4

(1117) SNP-based Prenatal Cell-free DNA Screening in Twin Pregnancies: A New Standard of Care?

Wednesday, February 14, 2024

1:00 PM – 2:30 PM

Location: Prince George's Exhibit Hall CDE, Lower Atrium Level

Primary & Presenting Author(s)

Ruben A. Quintero, MD (he/him/his)

USFetus Research Consortium
Coral Gables, FL, United States

Coauthor(s)

JH

Joseph Hurt, MD, PhD

University of Colorado, School of Medicine
Aurora, CO, United States
Neeta L. Vora, MD

Associate Professor
University of North Carolina
Chapel Hill, NC, United States
Neil S. Seligman, MD,MSCR

Associate Professor, Department of Obstetrics and Gynecology
University of Rochester Medical Center
Rochester, NY, United States
GR

Gerard Reilly, MD

Seven Hills Women's Health Center
Cincinnati, OH, United States
MW

Myra Wick, MD

Mayo Clinic
Rochester, MN, United States
SW

Samuel Wolf, DO

Emerald Coast Obstetrics and Gynecology
Panama City, FL, United States
Maeve Hopkins, MD, MA

Cleveland Clinic
Rocky River, OH, United States
TW

Tom Westover, MD

Capital Health
Trenton, NJ, United States
Homa K. Ahmadzia, MD, MPH

Assistant Professor
George Washington University
Washington, DC, United States
CK

Camille Kanaan, MD

Eastern Virginia Medical School
Norfolk, VA, United States
Andrei Rebarber, MD

Clinical Professor, Ichan School of Medicine at Mount Sinai
Icahn School of Medicine at Mount Sinai
New York, NY, United States
EK

Eftichia V. Kontopoulos, MD

USFetus Research Consortium
Coral Gables, FL, United States
JZ

Jingwen Zhang, PhD

Natera, Inc.
Austin, TX, United States
ME

Melissa Egbert, MS

Natera, Inc.
Austin, TX, United States
SV

Sophia Vourthis, MPH

Natera, Inc.
Austin, TX, United States
Vivienne Souter, MD

Research Director, Obstetrical Care Outcomes Assessment Program
Foundation for Health Care Quality
Seattle, WA, United States
Clark T. Johnson, MD, MPH (he/him/his)

Division Director-Maternal Fetal Medicine Assistant Professor
Sinai Hospital of Baltimore
Baltimore, MD, United States

Objective: Prenatal diagnosis of chorionicity is critical for the management of twin pregnancies. Although ultrasound has been recommended for this, it has not been thoroughly validated. SNP-based cell-free DNA (cfDNA) can determine zygosity from 9 weeks’ gestation. Dizygotic cfDNA infers dichorionicity (DC). Monozygotic (MZ) cfDNA results may require managing the pregnancy as monochorionic (MC), regardless of chorionicity. The purpose of this study was to assess the accuracy of the diagnosis of chorionicity by ultrasound (C-US) prior to knowledge of cfDNA results.

Study Design: Prospective observational registry multi-institutional study (13 sites in the USA). Inclusion criteria were an ongoing twin pregnancy (< 20 weeks’ gestation) with C-US prior to cfDNA. Exclusion criteria were higher order multiples, contraindication for cfDNA, and twin to twin transfusion syndrome prior to enrollment. C-US, cfDNA results, perinatal outcome and placental pathology reports were collected.

Results: A total of 137 twin pregnancies were enrolled in the study. After exclusions for undetermined zygosity on cfDNA (1), missing placental pathology (15), incomplete follow-up (11), and unreported chorionicity on ultrasound (4), 106 pregnancies remained. Median gestation at C-US was 11 weeks. Two of 28 (7.1%) pregnancies reported to be MC on pathology were DC on C-US. All were monozygotic on cfDNA. One in 78 pregnancies (1.3%) reported to be DC on pathology was MC on C-US and was dizygotic on cfDNA. Overall, chorionicity was misdiagnosed by C-US in 2.8% (3/106) of twin pregnancies. Of the MZ-cfDNA twins (41.5%, 44/106), 36% were DC and 64% were MC on pathology. All DZ cfDNA twins (62/106, 58.5%) were DC on pathology. Surgical pathology confirmed the cfDNA zygosity diagnosis in all cases.

Conclusion: Ultrasound assessment of chorionicity may be inaccurate in approximately 3% of twins. False negative MC diagnosis may preclude timely management of typical MC complications. False positive MC diagnosis may result in unnecessary surveillance or interventions. cfDNA screening for zygosity is essential in the management of twin pregnancies.