Grade and symmetry of normal fetal cortical development: a longitudinal two- and three-dimensional ultrasound study

Recent studies have shown the capability of ultrasound to demonstrate fetal cortical development. For practical application, it would be useful to have more insight into the physiological progress of cortical folding. A longitudinal study was undertaken to grade fetal cortical development and to study physiological asymmetry by means of a simple scoring system. The reproducibility of the scoring system and the differences between two-dimensional (2D) and three-dimensional (3D) ultrasound were also examined.

A cohort of 28 patients was examined by 2D and 3D ultrasound from 20 to 40 weeks of gestation. The development of selected fissures, sulci and cortical areas were graded from 0 to 5. One examination per week of gestation was randomly selected for evaluation of intraobserver and interobserver variation.

Two-hundred and fifteen ultrasound examinations were performed in 28 patients. The development of the different cortical areas is presented. The intraobserver and interobserver agreement for assessment of grade was good. Asymmetry was common between 24 and 28 weeks, especially in female fetuses. The right parieto-occipital fissure tended to be more advanced and the left calcarine and cingulate sulci tended to be more advanced. No clinically or statistically significant differences were found between 2D and 3D ultrasound.

Evaluation of cortical development by means of a simple scoring system is feasible and reproducible. Asymmetrical development of sulci, previously only described in vitro, has now also been demonstrated in vivo. 3D ultrasound was equally accurate and repeatable and no more time consuming than 2D ultrasound.