Fetal kidneys: additional sonographic criteria of normal development

The aim of this study was to establish objective criteria for the evaluation of cortical echogenicity (CE), cortical thickness (CT), and medullary thickness (MT), as well as the corticomedullary ratio (CMR), throughout gestation.

In this prospective single-center study, CE, MT, CT, and CMR were evaluated in a group of singleton pregnancies examined by ultrasound during the second and third trimesters.

The CE evolved from a hyperechoic pattern compared with the liver or spleen during early second trimester to a hypoechogenic pattern in the third trimester, with no fetus displaying cortical hyperechogenicity after 32 weeks. CT increased from 1.8 to 2.5 mm (p < 0.05) from 21 to 25 to 34 to 37 weeks; MT from 2.7 to 5.1 mm (p < 0.0001), and the CMR decreased from 0.7 to 0.5 (p < 0.001).

The CE, CT, and MT evolve with gestation. Cortical hyperechogenicity compared with the liver or spleen after 32 weeks or a CMR above 0.7 in the third trimester should raise the suspicion of a fetal nephropathy.