Congenital heart abnormalities are the most common structural birth defects, affecting fetal health and birth quality. The cardiovascular system begins forming at around 3 weeks of pregnancy, but full development isn't complete until 7-8 weeks. Exposure to adverse stimuli during this critical period can hinder development, potentially leading to congenital heart disease. Causes of fetal cardiovascular abnormalities include hereditary factors, fetal factors, and the maternal environment. Early detection is crucial, but early pregnancy ultrasound can be hindered by insufficient fetal development and fetal positioning. The second trimester offers a more stable period for fetal heart development and orientation, making it an ideal time for screening. Color Doppler ultrasound, using autocorrelation technology to color-code blood flow on a 2D image, provides several advantages: minimal trauma, no radiation, quick operation, and widespread clinical use. Its application extends beyond cardiology to various organs, including the brain, liver, spleen, stomach, kidney, breast, and uterus. In fetal screening, color Doppler clearly visualizes the heart's four chambers, cardiac veins and arteries, ventricular outflow tract, and blood vessels, improving detection rates. While color Doppler is widely used in China for prenatal screening, previous studies lacked large sample sizes and population representativeness. This meta-analysis aimed to comprehensively evaluate the diagnostic accuracy of color Doppler in detecting fetal cardiovascular abnormalities during the second trimester in the Chinese population.

Several studies have evaluated the clinical compliance rate of color Doppler in screening for fetal cardiovascular abnormalities during pregnancy. However, these studies were conducted with small sample sizes and were not representative of the general Chinese population. In addition, there have been few meta-analyses on the diagnostic accuracy of color Doppler in the diagnosis of fetal cardiovascular abnormalities during the second trimester in the Chinese population.

This systematic review and meta-analysis followed PRISMA and Cochrane Collaboration guidelines. English and Chinese databases (PubMed, Google Scholar, Cochrane Library, Clinical Trials, CNKI, Cqvip, WANFANG data, and Baidu scholar) were searched using keywords such as "cardiac abnormality," "heart anomaly," "heart disease," "congenital," "Color Doppler," "second trimester," "China," and "Chinese." Studies published between 2015 and 2022 were considered. Inclusion criteria included studies on Color Doppler in fetal cardiovascular abnormalities in China using human specimens and a two-stage screening process (questionnaire and physician diagnosis). Reviews, press releases, and studies with unclear diagnostic criteria were excluded. Data extraction included author, publication year, country, sample size, sensitivity, specificity, true/false positives/negatives. Study quality was assessed using the QUADAS-2 tool. Review Manager 5.3 was used for meta-analysis, employing a random-effects model to calculate pooled sensitivity, specificity, positive and negative predictive values. SROC curves and AUC were calculated to assess diagnostic test accuracy. Heterogeneity was assessed using the Cochrane Q test and I² statistic. The screening rate for each type of fetal cardiovascular abnormality was also calculated.

The initial search yielded 492 articles. After screening, 4 studies met the inclusion criteria, encompassing 151 patients with fetal cardiovascular abnormalities and 3397 controls. The pooled sensitivity ranged from 0.91 to 0.96, and the specificity was 1.00. The SROC curve showed an AUC >90%, classified as excellent. Seven types of fetal cardiovascular abnormalities were identified: tricuspid atresia, tetralogy of Fallot, atrioventricular septal defect, single ventricle, ventricular septal defect, single atrium, and endocardial pad defects. The highest screening rate was observed for atrioventricular septal defects (36%).

The high sensitivity and specificity, along with the excellent AUC, strongly support the clinical utility of second-trimester color Doppler ultrasound for diagnosing fetal cardiovascular abnormalities. The second trimester is optimal due to the stable fetal heart structure and reduced influence of fetal positioning. The results highlight the potential of color Doppler to improve early detection and facilitate timely interventions, improving birth outcomes and reducing the incidence of congenital heart disease. The study's findings on the high screening rate for atrioventricular septal defects warrant further investigation to understand the underlying reasons. While color Doppler is valuable, advancements in diagnostic techniques are still needed. Deep learning algorithms like EchoNet-Dynamic and DPS-Net, capable of automatically assessing cardiac function from echocardiographic videos and measuring ejection fraction, hold promise for improving diagnostic accuracy and efficiency in the future.

Second-trimester color ultrasound is a valuable diagnostic tool for detecting fetal cardiovascular abnormalities. Its high sensitivity and specificity make it suitable for clinical use in early diagnosis, contributing to better pregnancy outcomes. Further research with larger, multi-center studies is warranted to validate these findings and explore the potential of integrating advanced technologies like AI-powered image analysis into fetal cardiovascular screening.

The meta-analysis included only four studies, all conducted in the Chinese population, limiting the generalizability of findings. The detailed diagnostic processes after fetal induction or delivery were not fully described, which may have influenced the overall estimation. The exclusion of non-Chinese language publications might have introduced bias. Future research should involve larger, multicenter studies with detailed diagnostic information to strengthen these conclusions.