Developmental Changes of the Coronary Sinus Between the First and Second Trimesters

Objective To assess the coronary sinus (CS) presence, size, and CS to atrial ratio (CS/A) in the first trimester (FT) compared with the second trimester (ST). Methods In this IRB‐approved retrospective study, fetuses with adequate FT cardiac sweeps and normal ST hearts were included. Maternal and fetal characteristics were obtained. CS and atrial diameters were measured by a single sonologist. The CS/A ratio was compared between FT and ST. Linear regression assessed the relationship between biparietal diameter (BPD) and CS and atrial diameters. Statistical significance was set at P < .05. Results Among 99 fetuses, the CS was seen in 42/53 (79.2%) in the FT and 14/32 (43.8%) in the ST. No significant associations were found between CS visualization and the factors analyzed. The CS/A ratio was significantly higher in the FT versus ST (0.43 vs 0.25; P < .0001). Combined FT and ST data revealed positive correlations between BPD and both CS (slope = 0.018, P < .0001) and atrial diameters (slope = 0.135, P < .0001), suggesting differential growth rates, with the atrium exhibiting a faster growth rate as BPD increased. Conclusions The CS appears prominent in the FT compared with the ST, likely due to differential growth rates between the CS and atrium. Remnants of embryonic structures, differences in myocardial drainage, and hemodynamics may also be contributing factors. Larger prospective studies are needed to confirm these findings and assess the value of the FT CS/A ratio.