Diagnosis of fetal lung maturity by ultrasound: a new method and first results

The first results are presented of a method to determine the maturity of fetal lung by sonography. By comparing the frequency characteristics of lung echoes to those from the fetal liver as a reference organ, we avoid the known pitfalls which previously made it impossible to standardize fetal lung changes with gestation. We examined 222 patients between 27 and 39 completed weeks of gestation. In one ultrasound section we depicted fetal lung and liver simultaneously. Switching to A-mode we registered the frequencies contained in the video envelope in both organs. The registered frequencies were entered digitally in to a computer and checked for mean frequency, maximum frequency and minimum frequency. Afterwards, the ratio of the frequencies of the lung and liver were obtained. For all weeks of gestation, the mean value and standard deviation were calculated. We found the liver to be an adequate reference organ, since there is no change of the reflection pattern between the different weeks of gestation, while significant changes were registered in the fetal lungs. A quotient of Q(mean) lower than 1.1 suggests lung maturity, while values over 1.1 point to immaturity. This appeared to be confirmed in 13 patients who had agreement between amniotic fluid lecithin values and Q(mean). Further comparisons with amniotic fluid results will have to validate these findings.