First-Trimester Fetal Echocardiography: Identification of Cardiac Structures for Screening from 6 to 13 Weeks’ Gestational Age

Background Early fetal echocardiography (FE), performed at 12 to 16 weeks’ gestational age (GA), can be used to screen for fetal heart disease akin to that routinely performed in the second trimester. The efficacy of FE at earlier GAs has not been as well explored, particularly with recent advances in ultrasound technology. The aim of this study was to evaluate the efficacy of early FE in assessing fetal heart structure, and the added benefit of color Doppler (CD), from as early as 6 weeks through to 13⁺⁶ weeks’ GA. Methods Pregnant women were prospectively recruited for first-trimester FE. All underwent two-dimensional (2D) cardiac imaging combined with CD assessment, and all were offered second-trimester fetal echocardiographic evaluations. Fetal cardiac anatomy was assessed both in real time during FE and additionally offline by two separate reviewers. Results Very early FE was performed in 202 pregnancies including a total of 261 fetuses, with 92% (n = 241) being reassessed at ≥18 weeks’ GA. Mean GA at FE was 10⁺⁶ weeks (range, 6⁺¹ to 13⁺⁶ weeks). Transabdominal scanning was used in all cases, and transvaginal scanning was used additionally in most at <11 weeks’ GA (n = 103 of 117 [88%]). There was stepwise improvement in image resolution of the fetal heart in those pregnancies that presented at later gestation for assessment. CD assisted with definition of cardiac anatomy at all GAs. A four-chambered heart could be identified in 52% of patients in the eighth week (n = 12 of 23), improving to 80% (n = 36 of 45) in the 10th week and 98% (n = 57 of 58) by the 11th week. The inferior vena cava was visualized by 2D imaging in only 4% (n = 1 of 23) in the eighth week, increasing to 13% (n = 6 of 45) by the 10th week and 80% (n = 25 of 31) by the 13th week. CD improved visualization of the inferior vena cava at earlier GAs to >80% (n = 37 of 45) from 10 weeks. Pulmonary veins were not visualized by either 2D imaging or CD until after the 11th week. Both cardiac outflow tracts could be visualized by 2D imaging in the minority from 8⁺⁰ to 10⁺⁶ weeks (n = 18 of 109 [16%]) but were imaged in most from 11⁺⁰ to 13⁺⁶ weeks (n = 114 of 144 [79%]). CD imaging improved visualization of both outflow tracts to 64% (n = 29 of 45) in the 10th week. On 2D imaging alone, both the aortic and ductal arches were seen in only 29% of patients in the 10th week (n = 13 of 45), increasing to 58% when CD was used (58% [n = 26 of 45]) and to >80% (n = 47 of 58) using CD in the 11th week. Conclusions Very early FE, from as early as 8 weeks, can be used to assess cardiac structures. The ability to image fetal heart structures between 6 and 8 weeks is currently nondiagnostic. The use of CD significantly increases the detection of cardiac structures on early FE. The ideal timing of complete early FE, excluding pulmonary vein assessment, appears to be after 11 weeks’ GA.