Characterizing placental stiffness using ultrasound shear-wave elastography in healthy and preeclamptic pregnancies

Abstract

Purpose: To measure the stiffness of the placenta in healthy and preeclamptic patients in the second and third trimesters of pregnancy using ultrasound shear-wave elastography (SWE). We also aimed to evaluate the effect of age, gestational age, gravidity, parity and body mass index (BMI) on placental stiffness and a possible correlation of stiffness with perinatal outcomes.

Methods: In a case-control study, we recruited a total of 47 singleton pregnancies in the second and third trimesters of which 24 were healthy and 23 were diagnosed with preeclampsia. In vivo placental stiffness was measured once at the time of recruitment for each patient. Pregnancies with posterior placentas, multiple gestation, gestational hypertension, chronic hypertension, diabetes, autoimmune disease, fetal growth restriction and congenital anomalies were excluded.

Results: The mean placental stiffness was significantly higher in preeclamptic pregnancies compared to controls in the third trimester (difference of means = 16.8; 95% CI (9.0, 24.5); P < 0.001). There were no significant differences in placental stiffness between the two groups in the second trimester or between the severe preeclampsia and preeclampsia without severe features groups (difference of means = 9.86; 95% CI (-5.95, 25.7); P ≥ 0.05). Peripheral regions of the placenta were significantly stiffer than central regions in the preeclamptic group (difference of means = 10.67; 95% CI (0.07, 21.27); P < 0.05), which was not observed in the control group (difference of means = 0.55; 95% CI (- 5.25, 6.35); P > 0.05). We did not identify a correlation of placental stiffness with gestational age, maternal age, gravidity or parity. However, there was a statistically significant correlation with BMI (P < 0.05). In addition, pregnancies with higher placental stiffness during the 2nd and 3rd trimesters had significantly reduced birth weight (2890 ± 176 vs. 2420 ± 219 g) and earlier GA (37.8 ± 0.84 vs. 34.3 ± 0.98 weeks) at delivery (P < 0.05).

Conclusion: Compared to healthy pregnancies, placentas of preeclamptic pregnancies are stiffer and more heterogeneous. Placental stiffness is not affected by gestational age or the severity of preeclampsia but there is a correlation with higher BMI and poor perinatal outcomes.

Keywords: In vivo; Placenta; Preeclampsia; Shear-wave elastography; Ultrasound.

Fig. 1

B-mode images of SWE date acquisition in a healthy and b preeclamptic pregnancies. (1—Placenta, 2—fetus, 3—SWE data acquisition box, 4—chromatic scale of placental stiffness in kPa, 5—Q-box of measurements from the interrogated area)

Fig. 2

Flow diagram of patient recruitment at each stage of the study

Fig. 3

Placental stiffness measurement distribution at different gestational ages in the control and PE groups. Dotted line represents the optimal cut point (16.3 kPa) for the presence of preeclampsia determined by the ROC curve

Fig. 4

Box and whisker plots of placental stiffness in different trimesters and disease states.PE placentas were significantly stiffer than those of controls in the third trimester (P < 0.05).Dots represent median values for each group

Fig. 5

Heterogeneity of placental stiffness between peripheral and central location of the placenta. a There were no statistically significant differences in averaged placental stiffness between the central and peripheral regions in the control group. In contrast, the periphery of the placentas was significantly stiffer than that of the central region in PE patients (P < 0.05). b We found significant regional differences, while controlling for GA and maternal ages, between the control and PE groups. *Indicates statistically significant differences between groups (P < 0.05) and error bars in (a) and (b) are standard error of mean

Fig. 6

ROC curve calculating the optimized cutoff value of placental stiffness to indicate the presence of PE