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Quantitative Real‐time Cross‐sectional Echocardiography in the Developing Normal Human Fetus and Newborn

New high-resolution real-time ultrasound cross-sectional imaging systems have enabled us to demonstrate detailed fetal cardiac anatomy in the second half of pregnancy. We studied normal fetal cardiac development quantitatively by echocardiography in the second half of pregnancy in 69 normal pregnancies of healthy mothers. Eighteen of the fetuses were followed serially before birth. The estimated gestational ages were 20–41 weeks (mean 31.7 i 0.5 weeks [SEM]) of pregnancy. Calculated fetal weights were 500-3100 g (mean 1590 ± 83 g). Fetuses were reexamined within 36 hours after birth by real-time cross-sectional echocardiography to provide comparative data for the assessment of circulatory changes that take place at birth. Measurements of the right and left ventricles at the atrioventricular valve level were taken from four-chamber plane images of the heart before and after birth, and measurements of the aorta and pulmonary artery were taken in the short-axis view. All measurements were taken at end-diastole and were related to calculated fetal or actual newborn body weight. Statistical analysis for fetal cardiac dimension, right (RV) and left ventricular (LV) dimension and great artery size showed good correlation to calculated fetal weight, and growth curves for fetal cardiac structures were derived. Physiologic changes in the circulation at birth affected RV size considerably compared with measurements before birth. The RV/LV dimensional ratio was 1.18 ± 0.01 before birth and decreased to 0.99 ± 0.03 (p < 0.001) within 36 hours of birth. The pulmonary artery-to-aortic dimensional ratio did not change significantly after birth. Our findings about cardiac growth and the major adjustments of the circulatory system for extrauterine life are similar to those previously reported in humans and animals.