Congenital anomalies affect 2-3% of newborns and are major contributors to morbidity and mortality. The routine second-trimester (20-week) ultrasound scan is the main current standard screening tool and detects about two-thirds of these cases. Most fetal organogenesis is completed by 10 weeks, and advances in high-resolution imaging now allow earlier anatomical assessment during pregnancy. Many major anomalies can be identified at 11-14 weeks. As a result, international guidelines increasingly support screening of first-trimester anomalies. However, most countries, like England and the USA, still do not have formal recommendations. In England, early scans assess nuchal translucency, gestational age, and viability, but anatomical screening varies. Â A recent study published in PLOS Medicine aimed to determine whether incorporating systematic first-trimester anatomical assessment improves early detection rates of major congenital anomalies.
This population-based study followed the reporting of studies conducted using observational, routinely collected data (RECORD) recommendations. This study was carried out in two stages. First, a nationwide survey was conducted across all NHS maternity hospitals in England to document current first-trimester ultrasound protocols. This survey was developed in collaboration with the Fetal Anomaly Screening Program (FASP) and underwent multistage validation. This study was distributed to 131 NHS trusts. Second, survey findings were associated with the national congenital anomaly and rare disease registration service (NCARDRS) data to evaluate how different first-trimester screening policies impacted the timing of diagnosis for major congenital anomalies between 2017 and 2019. Statistical analysis was used for comparison of diagnostic timings before 16 weeks, after 2 weeks, and between 16 and 23+6 weeks.
A total of 118 responses were received from 110 NHS trusts (response rate = 84%). These responses were analyzed descriptively and categorized into four protocol groups based on the extent of anatomical assessment, such as group A (n = 27), group B (n = 22), group C (n = 45), and group D (n = 16). Despite a lack of national guidelines, approximately 75% of NHS trusts (83 centers/110) routinely perform assessments of first-trimester anatomy, including bladder, neck, kidneys, fetal head, spine, stomach, thorax, cord insertion, heart, and face. All these centers used the trans-abdominal imaging techniques and scheduled 20-30 minutes for first-trimester scans.
NCARDRS data identified 6,808 fetuses (from 1,030,224 pregnancies) across the 110 NHS trusts between April 2017 and March 2019. Out of 6,808 fetuses, 913 were excluded because of early fetal loss, unknown diagnosis age, and late booking for first-trimester screening. Hence, the remaining 5,895 fetuses with one of 14 anomalies were analyzed. Among these,  1,929 (32.7%, 95% confidence interval [CI] 31.5–33.9) were detected before 16 weeks. Early detection rates were lowest in group A (27.7%, 95% CI 25.4–30.0) whereas increased progressively in group B (31.2%, 95% CI 28.5–34.1), group C (33.2%, 95% CI 31.3–35.2), and group D (40.4%, 95% CI 37.3–43.4), showing a significant trend (P <0.0001).
Gastroschisis, acrania, and exomphalos were frequently identified early across all protocols, whereas major cardiac defects, limb reduction defects, and spina bifida were identified significantly more often across centers using detailed first-trimester protocols. Analyses were performed by protocol group, as hospital-level factors like patient risk and sonographer expertise may influence the detection rates.
In conclusion, detailed first-trimester screening significantly improves early detection of major anomalies in pregnant women. Despite wide variation across England, these population-level findings support the development of standardized national guidelines to enhance timely diagnosis and reduce inequities in prenatal care.
Reference: Karim JN, Broughan JM, Aldridge N, Pandya P, McHugh A, Papageorghiou AT. Impact of first-trimester ultrasound on early detection of major fetal anomalies: Nationwide population-based study of over 1 million pregnancies. PLoS Med. 2025;22(11):e1004709. doi:10.1371/journal.pmed.1004709
