Echogenicity of fetal lung and liver quantified by the grey-level histogram width

Grey-level histogram width (GLHW) values of fetal lung and liver were studied in 52 healthy fetuses in 24 to 38 weeks of pregnancy, comparing them to the mean grey level (MGL), grey-level standard deviation (GLSD) and the coefficient of variation (GLCV). Fetal lung GLHW was larger in 30–38 weeks than at 24–29 weeks, but there was no change in liver GLHW. GLHW was smaller in fetal lung than in the liver in 24–29 weeks, with no difference in 30–38 weeks. The lung/liver GLHW ratios were less than 1 in 24–29 weeks, but they were 1 or more in 30–35 weeks. Both MGL of fetal lung and liver showed linear increases during pregnancy, but no difference was found between the two. Fetal lung GLSD tended to decrease during pregnancy. The GLCV values of fetal lung and liver decreased during pregnancy, and differed between 24–29 weeks and 30–38 weeks, whereas there was no difference between fetal lung and liver. The correlation coefficients of GLHW and MGL of fetal lung and liver to the weeks of pregnancy were moderate, and the coefficients of GLSD and GLCV to the weeks of pregnancy were small. In conclusion, quantitatively measured echogenicity of fetal lung increased in 30 or more weeks of pregnancy, and suggested antepartum changes of fetal lung tissue. The GLHW is reliable, because it was reproducible in various gain settings of various ultrasonic imaging devices. The MGL, GLSD and GLCV are less reliable, because the grey level varied by the gain changes among various machines.