Background
Advances in ultrasound technology, in particular three-dimensional (3D) imaging with rendering, are enabling the boundaries of fetal assessment to be pushed further into the first trimester. However, 3D ultrasound is not used routinely, and its feasibility for routine first trimester anatomical assessment is unknown. Furthermore, new rendering technologies must be validated using an appropriate ‘gold-standard’ to be clinically useful.

Aims
To use novel embryological imaging methods to identify fetal structures visualised using 3D ultrasound in the first and early second trimesters. To assess the confidence and reproducibility of imaging normal fetal anatomical structures using two-dimensional (2D) and 3D ultrasound with novel rendering. Finally, to create an ex-vivo imaging environment mimicking in-utero conditions for assessing post-mortem fetal anatomy with 3D ultrasound.

Methods
A prospective cohort observational study at Queen Charlotte’s and Chelsea Hospital, London (2017-2020). Weekly ultrasound examinations were performed on 23 consecutively recruited participants from 8 to 17 weeks gestation and a single ultrasound examination was performed on 167 participants between 12 and 14 weeks gestation. Following 2D ultrasonography, 3D volumes were acquired and rendered. Fetal structures visualised in 3D were validated using embryological models and the confidence of imaging anatomical structures in 2D, 3D and a combined 2D plus 3D approach was assessed using an anatomical protocol.

Results
3D ultrasound with novel rendering and embryological correlation, enables comprehensive identification of fetal anatomy from 8 to 17 weeks gestation. A 2D plus 3D imaging approach significantly improves the confidence of imaging fetal anatomy compared to 2D ultrasound alone (p<0.0001). These findings are reproducible (Cohen’s kappa >0.9). Finally, ex-vivo 3D ultrasound also enables assessment of fetal anatomy.

Conclusion
This study confirms the feasibility of using 3D ultrasound to visualise fetal anatomy in the first and early second trimesters. 3D ultrasound used alongside 2D, aids reliable assessment of fetal anatomy.