Purpose Pregnancy complications such as preeclampsia and fetal growth restriction are sometimes thought to be caused by placental abnormalities associated with reduced oxygenation. Oxygen-enhanced MRI (R1 contrast) and BOLD MRI (R2* contrast) have the potential to noninvasively investigate this oxygen environment at a range of gestational ages. Methods Scanning was carried out at 1.5 T under maternal air and oxygen breathing in a single placental slice in 14 healthy pregnant subjects of gestational ages 21-37 weeks. We report R1 changes using a respiratory-triggered inversion recovery-turbo spin-echo sequence, which is sensitive to changes in PO2, and R2* changes using a breathhold multiple gradient-recalled echo sequence sensitive to changes in oxygen saturation. Results Significant R1 increases (P <0.005, paired t-test) and R2* decreases (P <0.0001, paired t-test) between air and oxygen breathing were demonstrated. ΔR1 decreased with gestational age (P <0.0005, r = -0.835, Pearson correlation test). No significant effect of gestational age on R2* change was observed. Conclusion The results demonstrate the feasibility of non-invasive investigation of placental oxygenation using MRI and the sensitivity of R 1 oxygen-enhanced MRI to gestational age. The techniques have the potential to provide unique noninvasive biomarkers in compromised pregnancies. Magn Reson Med 70:1427-1433, 2013. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.