MR Imaging Measurements of Altered Placental Oxygenation in Pregnancies Complicated by Fetal Growth Restriction

Abstract

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.

T2*‐weighted placental MRI: basic research tool or emerging clinical test for placental dysfunction?

“…The largest studies found a strong negative correlation between baseline T2* and gestational age ,21,25,27 , while Ingram et al . found a non‐significant negative correlation and a small study on 14 pregnant women failed to demonstrate any correlation with gestational age.…”

“…The main purpose of these studies was to estimate the baseline T2* value in normal pregnancy and in pregnancy complicated by FGR. In addition, the hyperoxic placental T2* response (ΔT2*) has been addressed in five of these studies.…”

“…Five human studies were performed at 1.5 T and two human studies were performed at 3 T using multi‐echo gradient‐recalled‐echo sequences. However, the MRI protocols were different with regards to the number and values of the included echo times (Table S2).…”

“…and Armstrong et al . were based on 3D placental models and, in the remaining studies, the T2* value was based on a single slice only.…”

“…In normal pregnancies at term, the placental baseline T2* was estimated to be 47–58 ms at 1.5 T and 25 ms at 3 T (Figures and , respectively). The reproducibility of baseline T2* measurements at 1.5 T has been addressed by Sinding et al ,.…”