Analysis of placental perfusion using magnetic resonance imaging in murine pregnancies: The placenta is fundamentally a vascular organ which brings oxygen and nutrients to the developing conceptus, and serves to dispose of waste products. Placental perfusion is key to accomplish this essential function. The structure and function of the organ change with advancing gestational age to meet the growing metabolic demands of the fetus. It is unclear whether the physiological regional blood perfusion of the placenta changes as a function of gestational age. We report a longitudinal study to characterize normal placental perfusion as a function of gestational age in the murine pregnancy. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) was used to quantify placental perfusion from the maternal circulation at gestational days 13, 15 and 17. Both regional and global placental perfusion was measured. The diameter of the maternal central canal of the placenta was also measured from the MRI data. Seven CD-1 pregnant mice were imaged longitudinally at 13, 15 and 17 gestational days (GDs) and measurements taken. We reported an increase in perfusion between GD 13 and GD 17 in one of the placental sub-regions, closely corresponding to the labyrinth zone. Whole placental perfusion also increased. Maternal central canal diameter also increased between GD 13 and GD 17 by almost 40%. The central canal diameter is functionally similar to the spiral arteries of the human placenta. The study showed that placental perfusion indeed increased with advancing gestation, especially in the labyrinth zone which is directly supplied by the central canal. Since the central canal diameter also increased in diameter, we propose that increased placental perfusion is driven by changes in maternal vascular features. 2. Quasi-static Elastography of the Uterine Cervix: A sonographic short cervix is the most powerful predictor of spontaneous preterm delivery. However, only a fraction of patients with a short cervix eventually have a preterm delivery. A short cervix may represent unscheduled cervical ripening in which the consistency of the cervix changes so that it is soft and compliant. Cervical length does not provide information about the biophysical properties of the cervix, but shear-wave elastography can. We report this year a longitudinal study to evaluate the elastic properties of the cervix and their association with preterm delivery. Cervical stiffness/softness was determined by ultrasound elastography to estimate the deformation or strain of the tissue when a mechanical compression is applied. A total of 545 patients were evaluated between 11-28 weeks of gestation; the prevalence of preterm delivery <37 weeks was 8.2% (n=45), and the prevalence of preterm delivery <34 weeks of gestation was 3.8% (n=21). We found that that women with high strain or deformation (3rd or 4th quartile) had a higher risk of preterm delivery <34 weeks and <37 weeks (OR 9.0; 95% CI, 1.1-74.0; P=0.02) than women with low strain (stiff cervix). As importantly, we found that patients with a stiff cervix were unlikely to deliver preterm. This suggests that elastography may be an adjunct technique to assess the risk of preterm delivery in patients with a sonographic short cervix. The potential benefit of this is the avoidance of interventions such as medical and surgical treatment (e.g. cervical cerclage).
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