Timing of detection of anencephaly in The Netherlands

Objective: The objective of this study is to assess the gestational age at detection and prevalence of anencephaly in the North of The Netherlands over a 5-year period. Methods: A case list of all cases of anencephaly from two fetal medicine units was compiled. Cases were included if the estimated due date was between 1 August 2008 and 31 July 2013. Results: Overall prevalence of anencephaly was 5.4 per 10.000 pregnancies (n=110). The majority of cases (69%) was detected before 18 weeks' gestation. Factors determining successful early diagnosis were competence level of the sonographers, with a significantly higher detection rate when scans were performed by a sonographer licensed by the Fetal Medicine Foundation (FMF) for nuchal translucency measurement (p=0.001), and gestational age at or beyond 11weeks of gestation (p=0.024). Conclusion: Improving detection of anencephaly in the first trimester requires ultrasound screening at or after 11weeks of gestation, performed by experienced sonographers trained in recognizing fetal anomalies. Sonographers should be instructed that the goal of the first trimester scan is not only to measure nuchal translucency thickness but also to exclude major anomalies.