Evaluation of fetal brain development in growth restriction subtypes using brain MRI volume measurement

This retrospective study aims to explore the value of brain MRI volume measurements in evaluating fetal brain development in fetal growth restriction (FGR) fetuses, by comparing 2 subtypes of FGR with appropriate gestational age (AGA) fetuses.

A total of 169 fetal brain MRI with suspected abnormal development, identified through ultrasound screening at this hospital between 2021 and 2025 were analyzed,11 cases were excluded. 98 cases were FGR fetuses (43 early-onset subtypes and 55 late-onset subtypes), and 60 were AGA fetuses, gestational age ranging from 26 to 37 weeks. Three-dimensional reconstruction and image segmentation were performed on fetal intracranial tissues including cerebrum, cerebellum and brainstem. Changes in brain volume at different gestational weeks were analyzed to assess the development of fetal brain anatomical structures.

In both groups, the Pearson correlation coefficients for cerebrum, brainstem, and cerebellum volume with head circumference and gestational age were greater than 0.8, indicating a strong correlation. Across all gestational age subgroups (26-31 weeks), cerebral, brainstem, and cerebellar volumes were all significantly smaller in early-onset FGR fetuses than in AGA fetuses (independent-samples t-test; e.g., at 26-27 weeks: cerebrum 87.3 ± 9.2 cm³ vs. 113.2 ± 10.3 cm³, brainstem 1.7 ± 0.2 cm³ vs. 2.7 ± 0.3 cm³, cerebellum 3.3 ± 0.6 cm³ vs. 4.6 ± 1.0 cm³; all p < 0.05; early-onset FGR n = 43, AGA n = 30, analysed across three gestational age windows of 10 fetuses each). For late-onset FGR fetuses (32-37 weeks; n = 55 vs. AGA n = 30, analysed across three gestational age windows of 10 fetuses each), cerebral volume was significantly reduced compared with AGA fetuses across all gestational age subgroups (e.g., at 32-33 weeks: 160.1 ± 18.7 cm³ vs. 194.1 ± 18.2 cm³; p < 0.05), while there was no statistically significant difference in brain stem volume between late-onset FGR and AGA fetuses at 34 weeks(4.6 ± 0.7cm³ vs. 5.0 ± 0.5cm³; BH-FDR adjusted p = 0.228) or later(5.2 ± 0.7cm³ vs. 5.5 ± 0.6cm³; BH-FDR adjusted p = 0.206), nor in cerebellum volume at 36 weeks or later(14.0 ± 1.6cm³ vs. 15.5 ± 2.2cm³; BH-FDR adjusted p = 0.110).

MRI measurement of fetal brain volume can serve as a predictor of brain development in 2 subtypes of FGR. In early-onset FGR, volumes of the brainstem, cerebellum and cerebrum consistently showed smaller growth prior to 32 weeks. Late-onset FGR was characterized by persistently smaller cerebrum volume. Brainstem volume was no longer significantly different from AGA levels by 34 weeks, and cerebellum volume approached AGA levels after 36 weeks.