Since 2017, Henan Province has implemented a free prenatal screening initiative aimed at reducing the incidence of birth defects and enhancing the quality of the birth population. A key component of this initiative is the provision of free first-trimester ultrasound screening, commonly referred to as nuchal translucency (NT) screening, for pregnant women throughout the province. To ensure high-quality assessments, ultrasound physicians are required to undergo specialized technical training and obtain a maternal and infant healthcare technical assessment certificate. The screening is conducted on fetuses with a crown-rump length (CRL) ranging from 45 to 84 mm, corresponding to a gestational age of 11 to 13 weeks and 6 days. Transabdominal scans are conducted using either a 1–6 MHz or a 2–9 MHz probe. Participation in the screening necessitates that pregnant women provide signed informed consent. The primary examination includes evaluating the number of fetuses, fetal heartbeat, NT thickness, CRL, placental position, and amniotic fluid volume. In measuring NT thickness, three measurements are taken in the midsagittal section of the fetal head, neck, and upper chest, with the maximum value recorded.

Pregnant women with an NT ≥ 3 mm, suspected of developmental abnormalities during initial screening, should undergo further evaluation. A referral form must be issued to facilitate the transfer of these high-risk pregnant women to the appropriate institution for additional prenatal diagnosis through amniocentesis, in accordance with the written recommendations provided by the screening agency. Furthermore, all pregnant women with increased NT should be monitored throughout the postpartum period as necessary. Fetal outcome data for these cases were collected through questionnaire interviews, using the same methodologies as those previously published (20). This process included three follow-up visits at 20–24 weeks of gestation, 28–34 weeks of gestation, and 6 months postpartum. The Henan Provincial People’s Hospital serves as a prenatal diagnosis institution and is responsible for quality management and prenatal diagnosis within the free prenatal screening projects conducted by 76 prenatal screening centers in the southeastern region of Henan Province.

Data analysis and graphing were performed using SPSS version 25.0 and MedCalc version 15.2.2. Continuous variables are expressed as means ± standard deviations (SDs) and were compared using t-tests. Categorical data are presented as case counts, with the chi-square test performing percentage comparisons. Fisher’s exact probability method was applied when expected values were less than one. Receiver operating characteristic (ROC) curve analysis was used to assess the diagnostic value of indicators such as nuchal translucency (NT) thickness and maternal age, which facilitated the determination of optimal thresholds, as well as sensitivity and specificity. A significance level of p < 0.05 was considered statistically significant.

This study included 100,910 singleton pregnancies screened for NT between 1 July 2017 and 31 December 2021. Among these, 4,899 fetuses were identified with increased NT thickness (≥3.0 mm) through the electronic medical records system, resulting in an overall incidence of 0.49% over the 5-year period (see Table 1). We analyzed the pregnancy outcomes of these fetuses by synthesizing the results from three follow-up visits documented in the system. In 2022, a comprehensive telephone review was conducted to validate the follow-up results. Unfortunately, we lost contact with or received refusals from family members in 699 cases. Table 2 presents basic information for the remaining 4,200 fetuses and pregnant women. The mean (±SD) crown-rump length (CRL) and gestational age were 59.15 ± 8.56 mm and 12.33 ± 0.73 weeks, respectively. The majority of NT thickness measurements fell within the range of 3 to 4.9 mm, comprising 80.5% of the cases. Furthermore, maternal age was predominantly concentrated in the 20- to 34.9-year age group, accounting for 86.5% of the sample, while pregnant women of advanced maternal age (≥35 years) constituted 10.4% of the participants.

Pregnancy outcomes can be classified into two groups: 2,875 patients experienced normal pregnancies without defects (68.5%), while 1,305 patients had adverse outcomes, which included elective termination of pregnancy (TOP), spontaneous abortion (SA), therapeutic abortion (TA), and live births with malformations (31.5%; Table 3). The nuchal translucency (NT) thickness of fetuses in the adverse outcome group (5.05 ± 1.74) was significantly greater than that of fetuses in the normal group (3.68 ± 0.88, p < 0.0001). Furthermore, the average maternal age in the adverse outcome group (29.13 ± 5.73) was also higher than that in the normal group (27.60 ± 4.74, p < 0.0001). In addition, receiver operating characteristic (ROC) curve analysis demonstrated that NT thickness was a more effective predictor of adverse outcomes (area under the curve [AUC] = 0.760; 95% confidence interval [CI]: 0.747 to 0.773; sensitivity: 0.61; specificity: 0.80) compared to maternal age (AUC = 0.572; 95% CI: 0.557 to 0.587; sensitivity: 0.29; specificity: 0.82; Supplementary Figures S1A–C). The optimal cutoff value for NT thickness associated with an increased incidence of adverse outcomes was determined to be 4 mm. These findings suggest that NT > 4 mm may elevate the risk of adverse pregnancy outcomes.

Increased nuchal translucency (NT) thickness is frequently linked to fetal developmental abnormalities. To investigate this association, we summarized the NT ultrasound findings from both the normal and adverse outcome groups (see Table 4). Within the adverse outcome group, we identified 180 patients (13.6%) with significant structural abnormalities, including anencephaly, hydrocephalus, encephalocele, cardiac structural defects, spina bifida, thoracoabdominal defects, visceral eversion, limb developmental abnormalities, and other multisystem disorders. Notably, cardiac structural abnormalities represented the largest proportion, accounting for 3.5%. Furthermore, among the remaining 575 fetuses, we detected abnormal ultrasound soft markers, such as cystic hygroma, anasarca, facial abnormalities, ductus venosus flow abnormalities, and cystic hygroma again, which collectively constituted 43.4%. In contrast, within the normal group comprising 2,875 patients, only 68 (2.4%) exhibited abnormal soft markers. Data analysis suggests that these abnormal ultrasound soft markers may contribute to adverse pregnancy outcomes for fetuses with increased NT (refer to Supplementary Table S2).

Pregnant women with increased nuchal translucency (NT) thickness are recommended to undergo amniocentesis for prenatal diagnosis through karyotype analysis. We collected and analyzed the karyotype results of 547 fetuses that underwent this diagnostic procedure. Among these fetuses, 450 (82.3%) exhibited normal karyotypes, while 97 (17.7%) displayed abnormal karyotypes, as detailed in Table 5. The identified abnormalities primarily consisted of aneuploidies, including trisomy 21 (T21), trisomy 18 (T18), trisomy 13 (T13), trisomy 9 (T9), and sex chromosome abnormalities. Notably, T21, commonly known as Down syndrome, represented the largest proportion of abnormalities, accounting for 7.1%. Within the cohort of 450 patients with normal karyotypes, 433 had normal pregnancies, whereas 17 chose elective termination of pregnancy (TOP). In contrast, among the 97 patients with abnormal karyotypes, 93 underwent TOP, leaving 4 who had normal pregnancies attributed to benign chromosomal polymorphisms.

The measurement of nuchal translucency (NT), along with the assessment of fetal trunk and head volume, is predominantly conducted during the first trimester. This approach is particularly effective at identifying conditions such as anencephaly, spina bifida, and other significant structural malformations. While the importance of NT screening is well recognized, its indications for detecting chromosomal abnormalities are limited, primarily serving as a preliminary basis for further prenatal diagnostic procedures (21). In contrast, serological screening is typically performed during both the first and second trimesters of pregnancy. Its affordability is a key advantage; however, it primarily screens for trisomies 21, 18, and 13, as well as neural tube defects, and is associated with elevated rates of false positives and false negatives (22). Non-invasive prenatal testing (NIPT), which uses high-throughput sequencing, has gained widespread adoption for the detection of fetal chromosomal aneuploidy. Although its cost is somewhat higher than that of the first two methods, NIPT offers the highest screening accuracy for aneuploidies, such as trisomy 21, achieving approximately 99% accuracy. Nevertheless, challenges such as sequencing read length, coverage limitations, reference bias, and population polymorphism can affect detection performance and early detection capabilities. With advancements in high-resolution technologies and the integration of artificial intelligence, including machine learning, NIPT is expected to provide more comprehensive genetic data, thereby facilitating the screening of copy number variations (CNVs) and single-gene variations that may be pathogenic or potentially pathogenic to the fetus (23–25). Importantly, the combination of these three screening methods can significantly enhance the accuracy of chromosomal abnormality detection (26–28).

Increased nuchal translucency (NT) is positively correlated with the risk of fetal developmental abnormalities; hence, NT ultrasound examination is widely used in first-trimester prenatal screening (29). Currently, two primary criteria exist for defining increased NT. In certain countries, increased NT is defined as values exceeding the 95th (30–32) or 99th (33, 34) percentiles of the NT distribution for a crown-rump length (CRL) ranging from 45 to 84 mm. Other countries utilize thresholds of ≥2.5 mm (35, 36), ≥3 mm (37, 38), or 3.5 mm (39, 40) as indicators of increased NT, with NT ≥3 mm being commonly adopted in China (41). Since 2017, free NT screening has been incorporated into government-funded programs, supported by an established electronic medical records system in Henan, China. A study utilizing this system analyzed the incidence of increased NT and its correlation with pregnancy outcomes in over 1 million singleton pregnancies, representing approximately 90% of all pregnant women in the southeastern region of Henan Province. In our study, we identified 4,899 patients with NT ≥3 mm, resulting in an incidence rate of 0.49%, which aligns with previous reports from Shanghai, China (42). Prior studies have demonstrated that increased NT is associated with adverse pregnancy outcomes, including a heightened risk of structural and chromosomal abnormalities. Consequently, a comprehensive follow-up study was conducted on fetuses with increased NT, monitoring their health status from 6 months to 5 years post-birth. Among the 4,200 fetuses with follow-up results, outcomes were categorized into two groups: 2,875 cases of normal pregnancies without defects and 1,305 cases of adverse pregnancy outcomes. The adverse outcomes included elective termination of pregnancy (TOP), spontaneous abortion (SA), threatened abortion (TA), and live births with malformations. In addition, among the 547 fetuses undergoing karyotype prenatal diagnosis, 450 exhibited normal results, while 97 were identified with chromosomal abnormalities. Trisomy 21 emerged as the most prevalent chromosomal abnormality. Follow-up results for the 450 fetuses with normal karyotypes indicated that approximately 96% of these pregnancies proceeded without complications, with only approximately 4% resulting in adverse outcomes. In contrast, nearly all fetuses with chromosomal abnormalities experienced negative pregnancy outcomes. These findings suggest that while increased nuchal translucency (NT) is closely associated with fetal chromosomal abnormalities, using an NT threshold of ≥3 mm for screening still captures a significant number of fetuses with normal chromosomal profiles.

In this study, we used receiver operating characteristic (ROC) curves to evaluate the diagnostic significance of nuchal translucency (NT) thickness and maternal age in predicting adverse fetal outcomes. Our analysis identified optimal threshold values, revealing that an NT thickness greater than 4 mm and a maternal age exceeding 35 years correspond to an approximate 38 and 10% increase in the risk of adverse outcomes, respectively. Furthermore, when both criteria were simultaneously met, the risk of adverse pregnancy outcomes escalated by more than 50%. These findings underscore the potential implications of NT thickness and maternal age in assessing the risk of adverse fetal outcomes.

Among 4,200 fetuses with increased nuchal translucency (NT), 180 cases of major developmental abnormalities involving multiple organ systems were identified. The predominant abnormality involved cardiac structures, accounting for 3.5% of cases, which included conditions such as Tetralogy of Fallot, single atrium/ventricle, cardiac ectopia, and various valve defects. Furthermore, abnormal ultrasound soft markers were observed in 43.4% of fetuses within the adverse outcome group, in contrast to only 2.4% in the normal outcome group. These soft markers included anasarca, facial abnormalities, ductus venosus flow abnormalities, hydrothorax, diaphragmatic hernia, and cystic hygroma. Subsequent analyses indicated that the presence of these soft marker abnormalities significantly elevated the risk of adverse pregnancy outcomes in fetuses with increased NT, as corroborated by the existing literature. For instance, the absence of the nasal bone has been associated with an increased risk of trisomy 21 (43). In addition, abnormal ductus venosus flow is linked to chromosomal abnormalities and congenital heart disease (44, 45). These findings underscore that the coexistence of ultrasound soft marker abnormalities and increased NT substantially heightens the risk of adverse pregnancy outcomes.