Altered Placental [1- 13 C]Pyruvate Metabolism in Spontaneous Intrauterine Growth Restricted near-term Pregnant Guinea Pigs

Abstract 1 IUGR is associated with increased risk of fetal compromise, yet can be difficult to detect and phenotype with routine clinical surveillance. Given placental insufficiency and hypoxia can remodel placental energy metabolism, methods that directly assess placental metabolic function may improve identification and phenotyping of growth-restricted pregnancies. We combined structural, body composition, and hyperpolarized metabolic MRI to characterize a near-term spontaneous IUGR (spIUGR) phenotype in the guinea pig. Twenty-two pregnant guinea pig sows (71 fetuses) underwent 1 H and hyperpolarized 13 C MRI at 60 ± 1 days gestation to quantify fetal and placental volumes, maternal/fetal body composition, and quantify placental pyruvate metabolism. Fetuses were classified as spIUGR when ≥ 3 of 5 established markers were present (body weight, brain–body, brain–liver, brain–placenta ratios, and body weight relative to pregnancy mean); corresponding volume cut-offs were derived from weight cut-offs. MRI-derived fetal and placental volumes correlated strongly with collection weights and classified spIUGR consistently with weight-based criteria. Maternal adiposity (subcutaneous and visceral) was inversely associated with fetal adipose tissue volume, and maternal visceral fat PDFF was negatively associated with fetal adipose PDFF. Hyperpolarized MRI demonstrated IUGR phenotype-dependent placental pyruvate routing: LPR increased with asymmetric (brain-sparing) growth, showing a positive association with brain–body volume ratio (p = 0.02) and brain–body weight ratio (p = 0.04). In contrast, BPR was not significantly related to brain–body ratios (p = 0.09–0.11) but was inversely associated with absolute fetal size (body volume and weight, p = 0.02). These findings validate MRI volumetry for non-invasive identification of placental insufficiency spIUGR and link growth restriction severity and asymmetry to distinct placental metabolic signatures measurable in vivo.