J Magn Reson Imaging. 2026 Aug 12. doi: 10.1002/jmri.70500. Online ahead of print.
ABSTRACT
BACKGROUND: Placental MRI has shown T2* decreases during contractions and increases during maternal hyperoxia. However, how contraction-induced placental oxygenation and deformation relate to uterine deformation and differ from hyperoxia-induced responses remains unknown.
PURPOSE: To quantify placental T2* and deformation changes during spontaneous non-labor uterine contractions and maternal hyperoxia, testing the hypothesis that contractions produce mechanically mediated placental responses distinct from hyperoxia.
STUDY TYPE: Retrospective.
POPULATION: Forty-nine MRI datasets from 46 pregnant participants with singleton pregnancies (24-39 weeks gestation).
FIELD STRENGTH/SEQUENCE: 3 T; dynamic multi-echo gradient-echo echo-planar imaging.
ASSESSMENT: Non-labor uterine contractions were defined as events lasting ≥ 0.5 min with peak uterine volume reduction > 2.5%. Placental T2* and deformation of the uterus, myometrium, placenta, fetus and amniotic fluid were quantified during normoxia (normal air, 21% O2, 5 min) with and without contractions, and maternal hyperoxia (100% FiO2, 4 min). Regional analyses were performed within and outside imaging-defined placental cotyledons.
STATISTICAL TESTS: Linear regression, linear mixed-effects models, Pearson correlation and paired t-tests (p < 0.05).
RESULTS: Complete contractions during normoxia were identified in 22 datasets, reducing placental T2* by 4.64 ± 0.75 ms. Maternal hyperoxia increased placental T2* by 11.36 ± 0.62 ms relative to normoxia. Significant gestational age-by-duration interactions were observed for contraction-associated placental deformation (β = 2.47 ± 1.04% points/min/week) and T2* reduction (β = 1.50 ± 0.44 ms/min/week). At baseline, cotyledons exhibited higher T2* than surrounding placental tissue (β = -11.56 ± 0.95 ms). Contractions significantly reduced the inside-outside cotyledon T2* difference (β = 3.14 ± 1.34 ms), whereas hyperoxia preserved regional heterogeneity (p = 0.48).
DATA CONCLUSION: Spontaneous non-labor uterine contractions induced coordinated decreases in placental volume and oxygenation that intensified with gestational age and contraction duration. In contrast, maternal hyperoxia produced larger, more uniform increases in oxygenation.
EVIDENCE LEVEL: 3.
TECHNICAL EFFICACY: Stage 3.
PMID:42581746 | DOI:10.1002/jmri.70500
