The coronary sinus in the fetus.
The normal coronary sinus drains venous blood from the cardiac veins to the right atrium. In some instances, the coronary sinus may be dilated due to volume or more rarely pressure overload. To assess the feasibility of detecting the coronary sinus in the fetus and to establish the normal values of the coronary sinus dimensions throughout gestation. Fetal echocardiography was performed in 78 normal fetuses from the 16th to the 40th week of gestation (median 25 week). The coronary sinus was measured in four-chamber view (87% of cases) or in parasternal short axis view equivalent (13%). A second group of nine fetuses with a dilated coronary sinus was compared to the normal group. Adequate imaging of coronary sinus was obtained in 97.4% of the normal fetuses. The diameter of the coronary sinus ranged from 1 to 3.2 mm (2 mm +/- 0.13 mm, mean +/- 5% confidence interval) and correlated well with the age of pregnancy (r = 0.86). The length-to-diameter ratio of 24% (+/- 6%) did not vary throughout pregnancy. All nine fetuses with a dilated coronary sinus had a persistent left superior vena cava which drained into it. The diameter of the coronary sinus was approximately three times larger in the abnormal group with a diameter-to-length ratio of approximately 83% (P < 0.0001). The coronary sinus is readily identified in the fetus. It gradually increases during pregnancy. An abnormal coronary sinus is easily diagnosed and should prompt the sonographer to look for a persistent left superior vena cava.