Impact of first-trimester ultrasound on early detection of major fetal anomalies: Nationwide population-based study of over 1 million pregnancies

Abstract

Background: Major fetal anomalies are an important cause of perinatal morbidity and mortality. While routine second-trimester ultrasound screening around 20 weeks is the current standard, advances in imaging have enabled earlier anatomical assessment in the first trimester. Despite increasing practice of early screening in England, there is no national policy recommending first-trimester anatomical evaluation, and little is known about its impact on detection rates at population level. Our aim was to examine if different policies of fetal anatomical ultrasound practice have an impact on earlier diagnosis of major fetal anomalies.

Methods and findings: We conducted a nationwide, population-based study linking data from a national survey of first-trimester ultrasound protocols in all NHS maternity units in England with congenital anomaly registration data from the National Congenital Anomaly and Rare Disease Registration Service (NCARDRS) for pregnancies between April 2017 and March 2019. NHS trusts were classified into four protocol groups: no anatomical assessment, basic, advanced, and extended anatomical protocols. We evaluated the proportion of 14 predefined major congenital anomalies detected prior to 16 weeks' gestation across these groups. A total of 1,030,224 pregnancies were included from 110 NHS trusts (84% response rate), with 5,895 fetuses affected by one of the anomalies of interest. First-trimester anatomical assessment was routinely conducted in 75% of trusts, though the scope varied. Overall, 32.7% (95% CI 31.5-33.9) of anomalies were detected before 16 weeks, with detection rates increasing stepwise by protocol detail: 27.7% (95% CI 25.4-30.0) in trusts with no protocol to 40.4% (95% CI 37.3-43.4) in those with extended protocols (p < 0.0001 for trend). Conditions such as acrania, exomphalos, and gastroschisis were commonly detected early regardless of protocol, whereas for anomalies such as spina bifida, limb reduction defects, and major cardiac malformations, detection was significantly higher in centers employing detailed first-trimester anatomical protocols. Due to data access restrictions and confidentiality considerations, analyses were conducted at the level of protocol group rather than individual hospitals. Hospital-level characteristics, including sonographer expertise and patient population risk, could not be adjusted for and may act as confounders.

Conclusions: More detailed first-trimester anatomical screening protocols are associated with significantly higher early detection rates of major fetal anomalies. While current practices vary considerably across England, this study provides population-level evidence suggesting that systematic first-trimester screening could improve the timeliness of anomaly detection. These findings support the consideration of standardized national guidance to reduce inequity and enhance prenatal care.