Fetal Brain Growth in the Early Second Trimester

Abstract

Background and purpose: Recent advances in fetal MR imaging technology have enabled acquisition of diagnostic images in the early second trimester. Interpretation of these examinations is limited by a lack of familiarity with the developmental changes that occur during these early stages of growth. This study aimed to characterize normal fetal brain growth between the 12th and 20th weeks of gestational age.

Materials and methods: This study was conducted as an observational retrospective analysis. Data were obtained from a tertiary care center's PACS database. All fetuses included had late fetal MR imaging (>20 weeks) or postnatal MR imaging, which confirmed normality. Each MR image was manually segmented, with ROIs placed to calculate the volume of the supratentorial parenchyma, brainstem, cerebellum, ventricular CSF, and extra-axial CSF. A linear regression analysis was used to evaluate gestational age as a predictor of the volume of each structure.

Results: Thirty-one subjects with a mean gestational age of 17.23 weeks (range, 12-19 weeks) were studied. There was a positive, significant association between gestational age and intracranial, supratentorial parenchyma; brainstem cerebellum; intraventricular CSF; and extra-axial CSF volumes (P < .001). Growth was fastest in the supratentorial parenchyma and extra-axial CSF. Fetal sex was not associated with the volume in any of the ROIs.

Conclusions: This study demonstrates distinct trajectories for the major compartments of the fetal brain in the early second trimester. The fastest growth rates were observed in the supratentorial brain and extra-axial CSF.

FIG 1.

Representative example of ROIs in the brain of 12-week (A), 15-week (B), and 19-week-old fetuses (C). The supratentorial brain is labeled in dark blue; the ventricular CSF, in light blue; the extra-axial CSF, in green; the brainstem, in salmon; and the cerebellum, in yellow.

FIG 2.

Application of inclusion and exclusion criteria in a flow diagram.

FIG 3.

Absolute and relative volume growth per week. For each structure, absolute volume growth per week of GA (A) and relative volume growth per week (B) demonstrate relatively larger supratentorial growth during these early GAs.