Ultrasonographic prediction of clinical pulmonary hypoplasia: measurement of the chest/trunk-length ratio in fetuses

Pulmonary hypoplasia is involved in patients with various surgical diseases. The aim of this study was to evaluate the clinical usefulness of measurement of the chest/trunk-length ratio (C/T) for predicting pulmonary hypoplasia in patients with congenital anomalies, with the exception of mass-like lesions in the thorax such as diaphragmatic hernia and cystic lung diseases. For measurement of C/T on fetal ultrasound, the sagittal section of the body trunk, including the spine, was analyzed. C/T was calculated as the chest length, defined from the top of the thorax to the top of the diaphragm, divided by the trunk length, defined from the top of the thorax to the bottom of the urinary bladder. From 1986 to 2000, measurements of C/T were undertaken in 49 healthy fetuses from 17 to 37 weeks of gestation and 98 fetuses with congenital anomalies, with the exception of intra-thoracic mass lesions, omphalocele, and fetal hydrops. Pulmonary hypoplasia was clinically assessed by the following criteria: (1) a lung-to-birth-weight ratio of 0.012 or less; (2) patients who required high-frequency oscillatory ventilation with mean airway pressure of 15 cmH(2)O or more with pure oxygen and/or who died presenting respiratory failure without evidences of meconium aspiration, congenital pneumonia, sepsis or hyaline membrane disease. For a predicting value for pulmonary hypoplasia to be obtained, sensitivity, specificity, positive predictive value and negative predictive value were quoted between C/T in patients with pulmonary hypoplasia and those without pulmonary hypoplasia. Healthy fetuses revealed the mean value as 0.38 +/- 0.03, with no significant change after 20 weeks of gestation. Pulmonary hypoplasia was assessed in 25 fetuses with urethral atresia and stenosis, renal agenesis, polycystic kidney, cloacal anomalies, diaphragmatic eventration, bronchopulmonary foregut malformation, chest deformity, meconium peritonitis and sacrococcygeal teratoma. As a predicting value for pulmonary hypoplasia, 0.32 or less of the maximum value of C/T indicated good accuracy, with a sensitivity of 92.0%, specificity of 95.9%, positive predictive value of 88.5% and negative predictive value of 97.2%. Ultrasonic measurement of C/T is useful in predicting postnatal respiratory conditions with regard to pulmonary hypoplasia.