Objectives To compare the sonographic signs of spina bifida obtained on axial and sagittal views of the fetal head between 11 and 13+6 weeks of gestation. Methods This was a retrospective study including 27 cases of spina bifida and 1003 randomly selected controls. Indirect markers of spina bifida were evaluated on stored ultrasound images. Intracranial translucency (IT), ratio between the brainstem and the brainstem–occipital bone distance (BS/BSOB), and maxillo‐occipital (MO) line were assessed on sagittal view, whereas biparietal diameter (BPD), BPD to abdominal circumference ratio (BPD/AC), and aqueduct to occipital bone (aqueduct of Sylvius [AoS]) distance were measured on the axial plane. Reference ranges were developed, and cases of spina bifida were examined in relation to the reference range. Results On the sagittal view, detection rates for IT below the fifth percentile, BS/BSOB above the 95th percentile, and an abnormal MO line were 52.3%, 96.3%, and 96.3%, respectively. On the axial view, detection rates for BPD, BPD/AC, and AoS below the fifth percentile were 66.7%, 70.4%, and 77.8%, respectively. Conclusion The MO line and the BS/BSOB ratio appear to be the best indirect ultrasound markers of spina bifida and can be easily obtained during the routine first‐trimester scan.

IntroductionFirst‐trimester ultrasound is widely accepted as part of standard care in many countries. With improvements in equipment, expertise and increasing number of technical studies describing imaging techniques, the detection rate for major fetal anomalies in the first trimester continues to rise and can be as high as 60% in high‐risk populations.MethodsWe set out to create a systematic pictorial guide for trained ultrasound providers to describe the common anatomical structures that are identifiable in the first trimester with provided images. In addition to normal anatomical structures, a number of anomalies with high detection rates are listed.ConclusionA large proportion of the major fetal abnormalities can be detected in the first trimester. A systematic approach is essential to ensure that anomalies are equally likely to be detected for patients of any risk background.