Purpose To evaluate oxygen-enhanced and blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging parameters in normal pregnancies and those complicated by fetal growth restriction (FGR). Materials and Methods This case-control study was approved by the local research ethics committee. Informed consent was obtained from all subjects. From October 2010 to October 2015, 28 women with uncomplicated pregnancies (individualized birthweight ratio [IBR] >20th percentile and delivery >37 weeks) and 23 with pregnancies complicated by FGR (IBR <5th percentile and abnormal Doppler ultrasonography [US] studies) underwent MR imaging. Differences in placental longitudinal R1 (1/T1) and transverse R2* (1/T2*) were quantified, with subjects breathing either air or oxygen. The difference in R1 (ΔR1) after hyperoxia was converted to change in partial pressure of oxygen (ΔPo). Data were acquired prospectively, with retrospective interpretation of group differences (unpaired t tests). Diagnostic models were developed by using logistic regression analysis with gestational age as a covariate. Results The mean baseline R1 and R2* for normal pregnancies (R1: 0.59 sec, 95% confidence interval [CI]: 0.58 sec, 0.60 sec; R2*: 17 sec, 95% CI: 14 sec, 20 sec) were significantly different from those of pregnancies complicated by FGR (R1: 0.63 sec, 95% CI: 0.62 sec, 0.65 sec; R2*: 26 sec, 95% CI: 22 sec, 32 sec) (P < .0001). The ΔR1 showed a significant negative association with gestational age (P < .0001) in the combined cohort, with the FGR group having a ΔR1 that was generally 61.5% lower than that in the normal pregnancy group (P = .003). The area under the receiver operating characteristic curve for the differentiation between pregnancy complicated by FGR and normal pregnancy by using ΔPo, baseline R1, and baseline R2* was 0.91 (95% CI: 0.82, 0.99). Conclusion R1, R2*, and ΔPo were significantly different between normal pregnancies and those complicated by severe FGR. MR imaging parameters have the potential to help identify placental dysfunction associated with FGR and may have clinical utility in correctly identifying FGR among fetuses that are small for gestational age. A larger prospective study is needed to assess the incremental benefit beyond that offered by US. RSNA, 2017.

Objective Magnetic resonance imaging (MRI) of placental invasion has been part of clinical practice for many years. The possibility of being better able to assess placental vascularization and function using MRI has multiple potential applications. This review summarises up‐to‐date research on placental function using different MRI modalities. Method We discuss how combinations of these MRI techniques have much to contribute to fetal conditions amenable for therapy such as singletons at high risk for fetal growth restriction (FGR) and monochorionic twin pregnancies for planning surgery and counselling for selective growth restriction and transfusion conditions. Results The whole placenta can easily be visualized on MRI, with a clear boundary against the amniotic fluid, and a less clear placental‐uterine boundary. Contrasts such as diffusion weighted imaging, relaxometry, blood oxygenation level dependent MRI and flow and metabolite measurement by dynamic contrast enhanced MRI, arterial spin labeling, or spectroscopic techniques are contributing to our wider understanding of placental function. Conclusion The future of placental MRI is exciting, with the increasing availability of multiple contrasts and new models that will boost the capability of MRI to measure oxygen saturation and placental exchange, enabling examination of placental function in complicated pregnancies.

The placenta is crucial for life. It is an ephemeral but complex organ acting as the barrier interface between maternal and fetal circulations, providing exchange of gases, nutrients, hormones, waste products and immunoglobulins. Many gaps exist in our understanding of the detailed placental structure and function, particularly in relation to oxygen handling and transfer in healthy and pathological states in utero. Measurements to understand oxygen transfer in vivo in the human are limited, with no general agreement on the most appropriate methods. An invasive method for measuring partial pressure of oxygen in the intervillous space through needle electrode insertion at the time of Caesarean sections has been reported. This allows for direct measurements in vivo whilst maintaining near normal placental conditions; however, there are practical and ethical implications in using this method for determination of placental oxygenation. Furthermore, oxygen levels are likely to be highly heterogeneous within the placenta. Emerging non‐invasive techniques, such as MRI, and ex vivo research are capable of enhancing and improving current imaging methodology for placental villous structure and increase the precision of oxygen measurement within placental compartments. These techniques, in combination with mathematical modelling, have stimulated novel cross‐disciplinary approaches that could advance our understanding of placental oxygenation and its metabolism in normal and pathological pregnancies, improving clinical treatment options and ultimately outcomes for the patient.