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Poster Session 1

Category: Prematurity

Poster Session 1

(323) Adverse Obstetric and Neonatal Outcomes in Dichorionic Twins: Does Zygosity Play a Role?

Wednesday, February 11, 2026

10:30 AM - 12:00 PM

Submitting Author and Presenting Author(s)

Prisca C. Diala, MD (she/her/hers)

Department of Obstetrics and Gynecology, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States

Coauthor(s)

SK

Sara Khan, MD

Department of Pediatrics, Division of Neonatology, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
TB

Tra-Mi Bao, BS

David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
JD

Jared Duldulao, MD

Department of Pediatrics, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
JC

Jiayue Chen, MPH

Department of Urology, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
MS

Mehrnaz Siavoshi, MPH, MS

Department of Urology, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
LK

Lorna Kwan, BS, MPH

Principal Statistician
Department of Urology, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
NS

Neil S Silverman, MD

Professor
Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States
IP

Ilina Pluym, MD

David Geffen School of Medicine at University of California, Los Angeles (UCLA)
Los Angeles, California, United States

Objective:
To evaluate whether zygosity is associated with preterm birth risk and perinatal outcomes in dichorionic twin pregnancies.

Study Design:
We conducted a retrospective cohort study of dichorionic twin pregnancies delivered after 24-week gestation at two affiliated academic urban medical centers between 2016 and 2024. Zygosity was determined by noninvasive prenatal testing (NIPT), neonatal sex at birth, or inferred from in vitro fertilization (IVF) frozen embryo transfer records. The primary outcome was preterm delivery rate in monozygotic (MZ) versus dizygotic (DZ) twins; the secondary outcome was composite neonatal morbidity. Multivariable logistic regression identified predictors of preterm delivery and neonatal morbidity after adjusting for demographic and clinical factors.

Results:
Among 265 dichorionic twin pregnancies, 94% were DZ (n=249) and 6% MZ (n=16). Maternal and fetal characteristics—including age, body mass index (BMI), IVF status, hypertensive disorders (HD), gestational diabetes, fetal growth restriction (FGR), and anomalies—were similar between groups. Preterm delivery occurred in 51% of DZ and 44% of MZ pregnancies (p=0.40). A neonatal morbidity event occurred in 43% of DZ and 34% of MZ pregnancies (p=0.36). Severe FGR (aOR 5.09, 95% CI 1.54–16.83) and HD (aOR 1.70, 95% CI 1.16–2.51) were independent predictors of preterm delivery, while increased parity was protective (aOR 0.51, 95% CI 0.27–0.95, Fig 1). Predictors of neonatal morbidity were small for gestational age (aOR 1.77, 95% CI 1.01–3.11), IVF conception (aOR 1.72, 95% CI 1.04–2.84), HD (aOR 1.73, 95% CI 1.09–2.74), and preterm delivery (aOR 22.24, 95% CI 13.01–38.03, Fig 2).

Conclusion:
Zygosity did not significantly impact obstetric or neonatal outcomes in dichorionic twin pregnancies. Adverse outcomes were primarily driven by pregnancy-related factors such as FGR and HD. These findings suggest that adverse outcomes in dichorionic twin pregnancies are mainly driven by clinical factors rather than genetic twinning status.