First-trimester anomaly scan shows high accuracy for major birth defects

First-trimester anomaly scan shows high accuracy for major birth defects | Image Credit: © Alexander Raths - © Alexander Raths - stock.adobe.com.

Introduction

A first-trimester anomaly scan (FTAS) among low-risk patients has high sensitivity for first-trimester major congenital anomalies and lower sensitivity for all anomalies combined, according to a recent study published in the American Journal of Obstetrics & Gynecology.¹

Of pregnancies, 2.5% present with a congenital structural anomaly, with routine care including a second-trimester anomaly scan (SAS).² However, increasing data has indicated first-trimester ultrasound may be effective for detecting major congenital anomalies, allowing patients more time to make reproductive decisions.¹

Research limitations and nationwide screening

“Yet, these studies included ultrasounds from secondary or tertiary care settings, performed by experienced sonographers, which makes it difficult to compare with a national prenatal screening setting,” wrote investigators.

All pregnant women in the Netherlands may receive prenatal screening including noninvasive prenatal test (NIPT) and an SAS at 18-weeks’ gestation. An FTAS was recently introduced to this program, and investigators conducted a nationwide cohort study to evaluate the benefits of this addition.

Study design

Certified sonographers performed the FTAS at 12+3 to 14+3 weeks’ gestation. Government reimbursement was provided for all prenatal tests except for NIPT.

Women receiving FTAS from November 1, 2021, to November 1, 2022, and with a dating scan before the FTAS were included in the analysis. Those with an abnormal NIPT before the FTAS or at high risk for fetal anomalies were excluded.

Referral to a tertiary care center was provided to women with suspicion of a fetal structural anomaly, fetal biometry percentile under 2.3 for any parameter, nuchal translucency of 3.3 mm or greater, absent fetal bladder, or longitudinal bladder diameter of 7 mm or more based on FTAS results. Outcome measures were normal, incomplete, or abnormal.

Evaluation metrics

Outcomes included uptake, test performance, and time to a final prenatal diagnosis. Patients with suspected abnormal findings or sonographers in doubt could be referred to a tertiary care center, allowing the performance of FTAS to be assessed in all anomalies diagnosed below 24-weeks’ gestation.

Anomaly subcategories included structural anomalies, genetic anomalies, other findings, and transient ultrasound findings. No overlap was reported. Patients with more than 1 structural anomaly in different organ systems were defined as having multiple congenital anomalies.

Uptake and test results

Of pregnancies, 74.9% underwent FTAS, with no difference in baseline characteristics reported based on FTAS results. Referral to a tertiary care center for a detailed diagnostic scan was reported in 1% of pregnancies.

True positive results were reported in 40.9% of cases, with 332 being structural anomalies, 117 genetic anomalies, 82 other findings, and 6 intrauterine fetal demise (IUFD). Termination of pregnancy (TOP) was performed in 50.1% of these cases.

Anomalies

Multiple congenital anomalies were the most common structural anomalies, identified in 21.7% of cases. This was followed by heart defects in 19.9%. A median 20 days was reported to diagnosis for structural anomalies, with a median gestational age of 16+3 weeks. Of these cases, 49.4% led to TOP, 6.6% IUFD, and 42.8% live births.

Trisomy was the most common genetic anomaly, identified in 38.5% of cases. A median 17 days to diagnosis was reported, at a median gestational age of 15+6 weeks. TOP was reported in 82.9% of pregnancies, IUFD in 9.4%, and live births in 7.7%.

Most other findings were sonomarkers or abnormal fetal biometry, with TOP reported in 6.1%, IUFD in 11%, and live birth in 82.9%. Of 1312 findings, 775 proved to be normal, with 586 having a normal first diagnostic scan and 189 anomalies on the FTAS that were resolved before 24-weeks’ gestation. Overall, the rate of false positives was 0.8%.

Sensitivity and conclusion

In comparison, the false negative rate was 68.4%, with 92.4% being diagnosed with structural anomalies and 6.9% with genetic anomalies. Overall, a sensitivity of 84.6% was reported for first-trimester major congenital anomalies.

“To evaluate the balance between benefits and potential harm of the FTAS 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,” wrote investigators.

References

1. Lust EER, Bronsgeest K, Henneman L, et al. Introduction of a nationwide first-trimester anomaly scan in the Dutch national screening program. Am J Obstet Gynecol 2025;232:396.e1-19. doi:10.1016/j.ajog.2024.07.026
2. Salomon LJ, Alfirevic Z, Berghella V. ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol. 2022;59(6):840-856. doi:10.1002/uog.24888