Systematic review of first trimester ultrasound screening in detecting fetal structural anomalies and factors affecting screening performance.

OBJECTIVES: To determine the sensitivity and specificity of first trimester ultrasound for the detection of fetal abnormalities; and to establish which factors might impact this screening. METHODS: Systematic review and meta-analysis of all relevant publications assessing the diagnostic accuracy of first trimester 2D (transabdominal and transvaginal) ultrasound in the detection of congenital fetal anomalies prior to 14 weeks gestation was performed. The reference standard used was the detection of abnormalities at birth or postmortem. Factors that may impact detection rates were evaluated including population characteristics, gestation, healthcare setting, ultrasound modality, use of an anatomical checklist for first trimester anomaly detection and what types of malformations were included in the study. In an effort to reduce the impact of study heterogeneity on results of the meta-analysis, data from the studies were analyzed within subgroups of major anomalies versus all types of anomalies; and low risk / unselected populations versus high risk populations. RESULTS: An initial electronic search identified 2,225 citations, from which a total of 30 relevant studies, published between 1991 and 2015, were selected for inclusion. For low risk or unselected populations (19 studies, 115,731 fetuses) the pooled estimate for detection of major abnormalities was 46.10% (95% C.I. 36.88-55.46). The detection rate for all abnormalities in low risk or unselected populations was 32.35% (95% C.I. 22.45-43.12), in 14 studies (97,976 fetuses); while the detection rate in high risk populations for the presence of all types of anomalies (six studies, 2,841 fetuses) was 61.18% (95% C.I. 37.71-82.19). Of the factors examined impacting detection rates there was a statistically significant relationship between the use of an anatomical protocol during first trimester anomaly screening and sensitivity for the detection of fetal anomalies in all subgroups (P < 0.0001). CONCLUSION: Detection rates for first trimester anomalies range from 32% in low risk, to over 60% in high risk groups. This demonstrates that first trimester ultrasound has the potential to identify a large proportion of fetuses affected with structural anomalies. The use of a standardized anatomical protocol improves the sensitivity of first trimester ultrasound screening for all anomalies and major anomalies in populations of varying risk. The development and introduction of international protocols with standard anatomical views should be undertaken, in order to optimize rates of first trimester anomaly detection