The echogenicity of the normal fetal kidneys during different stages of pregnancy determined objectively

To determine echogenicity of normal fetal kidneys during pregnancy by objective computerized method.

Computerized-based numerical method was developed, quantifying echogenicity of kidneys. 166 digital pictures of kidneys and liver were collected between 14 and 41 weeks of gestation. Calculating liver echogenicity was used to overcome gain problems. Women were healthy, delivered normal babies. Digital pictures were processed by software capable of identifying and labeling 256 shades of gray, numerically. In each picture, kidney was identified, region of interest was outlined. Average, standard deviation and entropy of pixel values were calculated and divided into three: 14-24, 24-36, 37-41 weeks of gestation: early, intermediate, late.

Mean color intensities were 70.2 ± 23, 50.6 ± 17, 47.3 ± 14 for early, intermediate, late groups, respectively (p < 0.0001, comparison between early and other groups). Standard deviation, which represents the echogenic homogenicity of the kidney, was 18 ± 4, 16.5 ± 3 and 17.2 ± 3 pixels for early, intermediate, and late, respectively (p = 0.003, between early and intermediate groups; p = 0.03, between the intermediate and late). Liver echogenicity remained constant throughout pregnancy.

Objective sonographic assessment of the echogenicity of the fetal kidney is presented here for the first time. It was found that kidneys are more echogenic during early pregnancy and more homogenous in appearance in mid-gestation.