Normative biometry of the fetal brain using magnetic resonance imaging

Abstract

The fetal brain shows accelerated growth in the latter half of gestation, and these changes can be captured by 2D and 3D biometry measurements. The aim of this study was to quantify brain growth in normal fetuses using Magnetic Resonance Imaging (MRI) and to produce reference biometry data and a freely available centile calculator ( https://www.developingbrain.co.uk/fetalcentiles/ ). A total of 127 MRI examinations (1.5 T) of fetuses with a normal brain appearance (21-38 gestational weeks) were included in this study. 2D and 3D biometric parameters were measured from slice-to-volume reconstructed images, including 3D measurements of supratentorial brain tissue, lateral ventricles, cortex, cerebellum and extra-cerebral CSF and 2D measurements of brain biparietal diameter and fronto-occipital length, skull biparietal diameter and occipitofrontal diameter, head circumference, transverse cerebellar diameter, extra-cerebral CSF, ventricular atrial diameter, and vermis height, width, and area. Centiles were constructed for each measurement. All participants were invited for developmental follow-up. All 2D and 3D measurements, except for atrial diameter, showed a significant positive correlation with gestational age. There was a sex effect on left and total lateral ventricular volumes and the degree of ventricular asymmetry. The 5th, 50th, and 95th centiles and a centile calculator were produced. Developmental follow-up was available for 73.1% of cases [mean chronological age 27.4 (±10.2) months]. We present normative reference charts for fetal brain MRI biometry at 21-38 gestational weeks. Developing growth trajectories will aid in the better understanding of normal fetal brain growth and subsequently of deviations from typical development in high-risk pregnancies or following premature delivery.

Keywords: Brain development; Centiles; Magnetic resonance imaging.

Fig. 1

Gestational age and sex distribution in the normal control cohort. Histogram of gestational age and sex distribution of MR scans in normal fetuses. Fetal gestational age was estimated from a first trimester dating ultrasound scan. f female, m male

Fig. 2

3D measurements: guidelines. 3D reconstructed brain of a normal control fetus at 32 gestational weeks with superimposed 3D segmentations of supratentorial brain tissue, lateral ventricles, cortex, cerebellum, and extra-cerebral CSF

Fig. 3

2D measurements: guidelines. a Brain biparietal diameter, b brain fronto-occipital length, c skull occipitofrontal diameter (c1) and skull biparietal diameter (c2), d head circumference using the eclipse tool, e transverse cerebellar diameter, f atrial diameter, g vermis height, h vermis width, and i vermis area

Fig. 4

3D measurements: growth trajectories and centiles. Best fit models for normal control 3D growth trajectories of a supratentorial brain tissue, b–d total and left and right lateral ventricles, e cortex, f cerebellum, and g extra-cerebral CSF. Solid lines depict the 50th centile, and dotted lines the 5th and 95th centiles. h Correlation of extra-cerebral CSF and supratentorial brain tissue volumes, eCSF extra-cerebral CSF

Fig. 5

2D measurements: growth trajectories and centiles. Best fit models for normal control 2D growth trajectories of a brain biparietal diameter, b brain fronto-occipital length, c skull biparietal diameter, d skull occipitofrontal diameter, e head circumference, f transverse cerebellar diameter, g extra-cerebral CSF, h atrial diameter, i vermis height, j vermis width, and k vermis area. Solid lines depict the 50th centile, and dotted lines the 5th and 95th centiles