Normative range of MRI-derived fetal brain volume throughout gestation: a prospective study

To establish normative ranges for fetal brain volume (FBV) and investigate its relationship with gestational age, using MRI to improve the understanding of fetal brain development.

A prospective, cross-sectional study.

A single-centre study conducted at a tertiary care hospital equipped with the world's only fetal-dedicated MRI system, located at Necker Hospital, Paris.

A total of 260 healthy singleton pregnancies between 16 and 36 weeks' gestation were included. Inclusion criteria required confirmed gestational age by first-trimester ultrasound, absence of fetal or maternal anomalies and no high-risk conditions impacting fetal growth.

T2-weighted fetal MRI scans were acquired using standardised protocols. Brain and cerebellar volumes were manually segmented using dedicated three-dimensional post-processing software, with volume calculations. Manual segmentations were performed by experienced raters. Intra-rater and inter-rater reproducibility were assessed on randomly selected subsets of 50 cases each, demonstrating excellent agreement (intraclass correlation coefficient>0.96 for both comparisons).

The primary outcome was the normative range of FBV by gestational age. Secondary outcomes included identifying variations in brain growth rates during gestation.

FBV increased significantly with gestational age, from a median of 20.1 cm³ at 16 weeks to 307.3 cm³ at 36 weeks. Growth rates showed the highest acceleration between 20 and 28 weeks' gestation, followed by a plateau. Linear regression demonstrated a strong correlation between FBV and gestational age (R²=0.95; p<0.001).

This study provides normative data on FBV, demonstrating consistent growth patterns during mid-to-late gestation. These findings highlight the potential for MRI to serve as a reference tool for monitoring fetal brain development and detecting anomalies in early pregnancy.