Ultrasound evaluation of biometric and Doppler parameters of kidneys in sheep in the prenatal and postnatal periods

The aim of this study was the ultrasound evaluation of kidneys in sheep fetuses during consecutive weeks of pregnancy and of lamb kidneys in the first two weeks after delivery. To evaluate the fetal kidneys, 20 singlepregnancy Suffolk sheep were examined. In the postpartum period, the kidneys were examined in 10 ewe lambs and 9 ram lambs. B-Mode ultrasound was used to assess the length, width and thickness of the kidney, as well as the thickness of the renal parenchyma and the renal cortex. Vascular haemodynamics was assessed with color and pulsed Doppler in renal, segmental and interlobular arteries. Fetal kidneys were visualized from 53 +/- 2.00 days, and corticomedullary differentiation was observed from the 10th week of pregnancy onwards. All fetal kidney biometric parameters increased significantly in the following weeks of pregnancy. The width and thickness of the kidneys were greater in male than in female fetuses (P < 0.05). The left kidney was thicker than the right kidney (P < 0.05). An interactive effect of gestational age, fetal sex and kidney location on kidney width, kidney thickness and renal parenchyma thickness (P < 0.05) has been demonstrated. All the biometric parameters of the kidneys differed significantly between the first and the second week of life of the lambs. The thickness of the renal cortex was greater in the ram lambs (P < 0.05). However, the length, width and thickness depended on the location of the kidneys (P < 0.05). An interactive effect of age, sex and kidney location on kidney width in lambs was demonstrated (P < 0.05). In the fetal renal artery, peak systolic velocity (PSV) and end-diastolic velocity (EDV) were significantly lower than in lamb kidneys in the first few days of life. In turn, the PSV/EDV and resistance index (RI) in fetal kidneys were significantly higher than that in newborn lambs. In lambs, PSV, PSV/EDV, RI and PI in the renal artery were significantly higher than that in the segmental and interlobular arteries. Regardless of the location of the arterial vessel, significant differences were noted between the Doppler indices in one-week and two-week-old lambs. The obtained results may be useful in establishing reference values for biometric and hemodynamic ultrasound parameters of sheep kidneys during the fetal and neonatal period. Assessment of the renal cortex is especially of great clinical importance. Increased echogenicity and reduced thickness may indicate certain pathological processes in the kidney. The results of Doppler indices indicate that the postnatal renal haemodynamics depends on the age of the lambs and the location of the renal vessels. Therefore, these factors should be taken into account in the assessment of renal arterial blood flow in lambs.