Uteroplacental Responses to Physiological Challenges Throughout Pregnancy Using MRI

Area of Science:

• Obstetrics and Gynecology
• Radiology
• Fetal Medicine

Background:

• Placental MRI reveals T2* changes during contractions and hyperoxia.
• The relationship between contraction-induced placental oxygenation/deformation and uterine changes, versus hyperoxia effects, is unclear.

Purpose of the Study:

• To quantify placental T2* and deformation during non-labor contractions and maternal hyperoxia.
• To test if contractions cause distinct mechanical placental responses compared to hyperoxia.

Main Methods:

• Retrospective analysis of 49 MRI datasets from 46 pregnancies (24-39 weeks gestation).
• Dynamic multi-echo gradient-echo echo-planar imaging at 3T.
• Quantified placental T2* and deformation during normoxia (with/without contractions) and hyperoxia, with regional analysis of cotyledons.

Main Results:

• Contractions decreased placental T2* by 4.64 ms; hyperoxia increased it by 11.36 ms.
• Contraction effects on placental deformation and T2* reduction intensified with gestational age and duration.
• Contractions reduced placental T2* heterogeneity between cotyledons and surrounding tissue, while hyperoxia did not.

Conclusions:

• Spontaneous contractions decrease placental volume and oxygenation, intensifying with gestation and duration.
• Maternal hyperoxia increases placental oxygenation more uniformly and to a greater extent than contractions.
• Contraction-induced placental changes are mechanically mediated and distinct from hyperoxia responses.