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Poster Session 1

Category: Physiology/Endocrinology

Poster Session 1

(118) Tocolytic Use and Altitude Exposure in Air Transport for Threatened Preterm Labor

Wednesday, February 11, 2026

10:30 AM - 12:00 PM

Submitting Author and Presenting Author(s)

Alixandria F. Pfeiffer, DO

Maternal-Fetal Medicine Fellow
University of Texas Health San Antonio
University of Texas health San Antonio, Texas, United States

Coauthor(s)

KL

Karissa Lonon, BA

University of Texas Health San Antonio
San Antonio, Texas, United States
KM

Katie McBee, BS, MPH

University of Texas Health San Antonio
San Antonio, Texas, United States
AM

Allison Moreno, BS, RN

University Health System
San Antonio, Texas, United States
Hadley Ross, MD

Maternal-Fetal Medicine Fellow
UT Health San Antonio
San Antonio, Texas, United States
Patrick S. Ramsey, MD, MSPH (he/him/his)

Professor, Vice Chair Inpatient Obstetrics
Department of Obstetrics and Gynecology University of Texas Health Science Center in San Antonio
San Antonio, Texas, United States
JB

John J. Byrne, MD, MPH

Assistant Professor
University of Texas Health Science Center in San Antonio
San Antonio, Texas, United States

Objective:
To evaluate whether pre-transport tocolytic use is associated with controlling uterine contractions during air transport among pregnant patients with threatened preterm labor (PTL), and secondarily to assess whether altitude exposure affects contraction patterns during transport.

Study Design:
We conducted a retrospective cohort study of pregnant patients ≥20 and < 37 weeks’ gestation transported via air to a tertiary maternal care center from 2020–2025. Altitude exposure was categorized as High ( >3000 ft), Low (≤3000 ft), or Unknown. The primary outcome was uterine activity pattern during transport (increased, unchanged, or decreased contractions per 10 minutes), focusing on identifying contraction control or reduction. Multivariable logistic regression assessed associations between pre-transport tocolytic use and contraction control, adjusting for gestational age, flight type (helicopter vs fixed-wing), insurance, and rurality. Secondary analyses evaluated whether altitude exposure was associated with contraction changes in the full cohort, helicopter-only subgroup, and cases with known altitude.

Results:
Among 185 air-transported patients, 113 were transferred for PTL (60 without tocolytics, 53 with). In adjusted analyses, pre-transport tocolytic use was not significantly associated with contraction control during transport (OR 0.74, 95% CI 0.36–1.71, p=0.53). Altitude documentation was available for 21 helicopter transports (Low=17, High=4). In the helicopter-only subgroup, altitude category was not significantly associated with contraction changes (Low vs High OR 1.14, p=0.91). In the full cohort model, altitude was also not significantly associated with uterine activity (Low vs High OR 1.11, p=0.93; Unknown vs High OR 0.53, p=0.55).

Conclusion:
Pre-transport tocolytic use was not associated with improved control of uterine contractions during air transport for PTL. Altitude exposure, including in helicopter-only and altitude-known subgroups, was not associated with contraction changes.