Characterization of uterine involution using B-mode ultrasonography, color Doppler and elastography (acoustic radiation force impulse) for assessing postpartum in Santa Inês ewes

Abstract

The aim of this study was to investigate uterine involution using ultrasonography techniques during postpartum. Postpartum ultrasonography evaluation (B-mode, color Doppler and Acoustic Radiation Force Impulse elastography) of the uterus was performed by transabdominal approach at immediate after birth and sequentially every 48 hours, during 30 days. The uterine echotexture did not present significant variations (P >0.05) being homogeneous in most evaluations; echogenicity of the uterus increased along the evaluation period (P =0.0452). Progressive and remarkable decrease of the total uterine diameter (UD) were observed (P <0.0001), especially during the first days postpartum. The thickness of uterine wall gradually decreased, as well the endometrial, myometrium and lumen diameters (P <0.0001). Uterine blood flow was assessed by Doppler and decreased during postpartum period, being significantly lower (P=0.0225) on the 30^th day of postpartum. Uterine parenchyma presented as homogeneous dark areas (not deformable) on qualitative ultrasound elastography and the means shear velocity values of the uterine wall on quantitative elastography did not differ. This is the first study that evaluate the stiffness of uterine wall in healthy ewes, providing baseline data about quantitative and qualitative stiffness of the normal uterus, and it may be a useful tool for early diagnosis of uterine alterations during the postpartum period, using the reference parameter established for the assessment of uterine integrity during postpartum period.

Keywords: puerperium; sheep; uterine involution; uterine stiffness.

Figure 2. Graphic illustration showing the relation between B-mode uterine measurements, uterine shear wave velocity (SWV) electrography evaluation and Postpartum days. The dots indicate the collected values, the black line the regression that explains the behavior and the dotted line the 95% confinement margin.

Figure 1. Ultrasound color Doppler image of uterine blood flow during postpartum in healthy ewes. Figure 1A,11C: 4, 18 and 30 DPP, respectively. Vessels in red are those that approach the transducer, that is, flow in the proximal direction; the vessels in blue are those that move away from the transducer, that is, flow in the distal direction. Mixed color images are areas of blood turbulence.

Figure 3. Qualitative uterine ARFI elastography analysis during postpartum. Note the B-mode image (left) and the image of the elastography (right) of the uterus showing a homogeneous and dark (hard) image, respectively.

Figure 4. Quantitative uterine ARFI elastography analysis during postpartum. Note the measurement of the shear velocity of uterine wall (Vs= 1.35 m/s), with the presence of a caliper for the portion assessed.