Introduction of a nationwide first-trimester anomaly scan in the Dutch national screening program

A significant proportion of major fetal structural anomalies can be detected in the first trimester by ultrasound examination. However, the test performance of the first-trimester anomaly scan performed in a low-risk population as part of a nationwide prenatal screening program is unknown. Potential benefits of the first-trimester anomaly scan include early detection of fetal anomalies, providing parents with more time for reproductive decision-making.

To investigate the uptake, test performance, and time to a final prenatal diagnosis after referral.

A nationwide implementation study was conducted in the Netherlands (November 2021-November 2022). The FTAS was performed between 12+3 and 14+3 weeks of gestation by certified sonographers using a standard protocol. Women were referred to a tertiary care center if anomalies were suspected. Uptake, test performance, and time to a final prenatal diagnosis (days between referral and date of final diagnosis/prognosis for reproductive decision-making) were determined. Test performance was calculated for first-trimester major congenital anomalies, such as anencephaly and holoprosencephaly and all diagnosed anomalies <24 weeks of gestation.

The first-trimester anomaly scan uptake was 74.9% (129,704/173,129). In 1.0% (1313/129,704), an anomaly was suspected, of which 54.9% (n=721) had abnormal findings on the detailed first-trimester diagnostic scan and 44.6% (n=586) showed normal results. In 0.5% (n=6), intrauterine fetal death occurred. In the total group of 721 cases with abnormal findings, 332 structural anomalies, 117 genetic anomalies, 82 other findings (abnormal fetal biometry, sonomarkers, placental/umbilical cord anomaly, an-/oligohydramnios), and 189 cases with transient findings (defined as ultrasound findings which resolved <24 weeks of gestation) were found, with 1 case having an unknown outcome. 0.9% (n=1164) of all cases with a normal first-trimester anomaly scan were diagnosed with a fetal anomaly in the second trimester. Test performance included a sensitivity of 84.6% (126/149) for first-trimester major congenital anomalies and 31.6% (537/1701) for all types of anomalies. Specificity for all anomalies was 99.2% (98,055/98,830); positive predictive value 40.9% (537/1312); negative predictive value 98.8% (98,055/99,219); positive likelihood ratio 40.3; negative likelihood ratio 0.7; false positive rate 0.8% (775/98,830), and false negative rate 68.4% (1164/1701). The median time to diagnosis for structural anomalies was 20 days (6-43 days; median gestational age 16+3), for genetic anomalies 17 days (8.5-27.5 days; median gestational age 15+6 weeks), and for first-trimester major congenital anomalies 9 days (5-22 days; median gestational age 14+6 weeks).

The performance of a newly introduced nationwide first-trimester anomaly scan in a low-risk population showed a high sensitivity for first-trimester major congenital anomalies and a lower sensitivity for all anomalies combined. The program was accompanied by a referral rate of 1.0%, of which 59.1% involved cases where anomalies were either not confirmed or resolved before 24 weeks gestation. Timing of diagnosis was around 16 weeks of gestation for referred cases. To evaluate the balance between benefits and potential harm of the first-trimester anomaly scan within a nationwide prenatal screening program, it is essential to assess the effectiveness of the program over time and to consider the perspectives of both women and their partners, as well as healthcare professionals.