Placental magnetic resonance imaging in chronic hypertension: A case-control study

Abstract

Introduction: We aimed to explore the use of magnetic resonance imaging (MRI) in vivo as a tool to elucidate the placental phenotype in women with chronic hypertension.

Methods: In case-control study, women with chronic hypertension and those with uncomplicated pregnancies were imaged using either a 3T Achieva or 1.5T Ingenia scanner. T2-weighted images, diffusion weighted and T1/T2* relaxometry data was acquired. Placental T2*, T1 and apparent diffusion coefficient (ADC) maps were calculated.

Results: 129 women (43 with chronic hypertension and 86 uncomplicated pregnancies) were imaged at a median of 27.7 weeks' gestation (interquartile range (IQR) 23.9-32.1) and 28.9 (IQR 26.1-32.9) respectively. Visual analysis of T2-weighted imaging demonstrated placentae to be either appropriate for gestation or to have advanced lobulation in women with chronic hypertension, resulting in a greater range of placental mean T2* values for a given gestation, compared to gestation-matched controls. Both skew and kurtosis (derived from histograms of T2* values across the whole placenta) increased with advancing gestational age at imaging in healthy pregnancies; women with chronic hypertension had values overlapping those in the control group range. Upon visual assessment, the mean ADC declined in the third trimester, with a corresponding decline in placental mean T2* values and showed an overlap of values between women with chronic hypertension and the control group.

Discussion: A combined placental MR examination including T2 weighted imaging, T2*, T1 mapping and diffusion imaging demonstrates varying placental phenotypes in a cohort of women with chronic hypertension, showing overlap with the control group.

Keywords: Chronic hypertension; Magnetic resonance imaging (MRI); Placenta.

Fig. 1

Example T2 weighted imaging and T2* maps in coronal and sagittal planes across gestation. On the left, the control panel depicts the following from left to right: T2-weighted imaging in the coronal plane, T2-weighted imaging in the sagittal plane, T2* map in the coronal plane and T2* map in sagittal plane. On the right, the panel depicts images from women with chronic hypertension and a placental mean T2* value below the 10th centile. Within the panel from left to right, images are in the following order: T2-weighted imaging in the coronal plane, T2 weighted imaging in the sagittal plane, T2* map in the coronal plane and T2* map in sagittal plane. Within the T2* maps, darker areas represent low T2* values while brighter orange-yellow areas high T2* values.

Fig. 2

Scatterplot of placental mean T2* at 3 T against gestational age at imaging, subdivided by birthweight centile at subsequent delivery to show Appropriate for Gestational Age (AGA) infants, and those Small for Gestational Age, divided into 3rd-10th centile, and those <3rd centile (A) in uncomplicated control group and (B) in women with chronic hypertension.

Fig. 3

Illustrative histogram plot of T2* values at the same gestation (27 weeks' gestation) for one woman from each of the following groups (A) the control group (B) with chronic hypertension (CHTN) and normal placental mean T2* (C) with chronic hypertension and a placental mean T2* less than the 10th centile for gestation (D) CHTN participant who developed superimposed preeclampsia (PE).

Fig. 4

Scatterplot of histogram derived measures of (A) skewness at 3T imaging, (B) skewness at 1.5T imaging, (C) kurtosis at 3T imaging and (D) kurtosis at 1.5T imaging against gestational age at scan with i) chronic hypertension ii) chronic hypertension at enrolment who subsequently developed superimposed preeclampsia after imaging iii) controls iv) preeclampsia at enrolment. For the presentation of results, we have included an additional dataset of women with preeclampsia imaged at 3T in whom we have previously reported enrolment and pregnancy outcome characteristics [27] and women with preeclampsia imaged at 1.5T in whom enrolment and pregnancy outcome characteristics are provided in Supplemental Tables S1 and S2.