A longitudinal study describing confidence limits of normal fetal cardiac, thoracic, and pulmonary dimensions from 20 to 40 weeks' gestation.

The current prospective, longitudinal study was designed to define the confidence limits and characteristics of growth for fetal cardiac, thoracic, and pulmonary dimensions from 20 to 40 weeks' gestation. We tested the hypotheses that (1) CC/TC, (2) CC/AC, (3) TC/HC, and (4) TC/AC ratios remain constant throughout this period of gestation. The four-chamber view of the fetal heart in diastole, in the absence of fetal breathing, was used as a standard reference for sonographic measurement of cardiac, thoracic, and left and right pulmonary dimensions in a longitudinal study of 45 uncomplicated pregnancies. Cardiac growth is best fit by a quadratic function: -8.147 + 0.900 (GA) - 0.0078 (GA)2. Similarly, thoracic growth is best fit by a quadratic function: -14.072 + 1.757 (GA) - 0.018 (GA)2. The characteristics of growth of the left and right lungs are best described by linear growth equations: -1.71 + 0.426 (GA) and -1.62 + 0.539 (GA), respectively. Each of the CC/TC, CC/AC, TC/HC, and TC/AC ratios changed significantly over time.