Effects of <scp>Mediterranean</scp> diet and stress‐reduction interventions during pregnancy on fetal brain development detected using magnetic resonance imaging

OBJECTIVE: To assess whether lifestyle interventions based on Mediterranean diet or stress reduction during pregnancy are associated with differences in fetal brain development detectable by two-dimensional magnetic resonance imaging (MRI) in a high-risk population for small-for-gestational-age neonates. METHODS: This was a secondary analysis of the randomized controlled clinical trial, Improving Mothers for a better PrenAtal Care Trial BarCeloNa (IMPACT BCN), which enrolled 1221 singleton pregnancies at high-risk for a small-for-gestational-age neonate between February 2017 and March 2020. At midgestation, participants were randomly allocated into three groups: a Mediterranean diet intervention; a stress-reduction program; or usual care. A randomly selected subgroup (n = 124) underwent fetal brain MRI between 36.1 and 39.1 weeks' gestation and were analyzed offline. Offline analysis included measurements of biparietal diameter, occipitofrontal diameter, cortical sulci depth, corpus callosum length, vermis height and cerebellar transverse diameter. Differences in brain measurement between groups were analyzed by regression models adjusted for baseline maternal characteristics, gestational age at MRI assessment, fetal sex, fetal head size and MRI scanner model. RESULTS: Fetuses in the Mediterranean-diet group (n = 36) showed a significantly deeper right insula (mean ± SD, 28.78 ± 1.16 mm vs 27.88 ± 1.23 mm; P = 0.03), a deeper left insula (mean ± SD, 28.60 ± 1.21 mm vs 27.49 ± 1.26 mm; P = 0.01) and a longer corpus callosum (mean ± SD, 42.24 ± 2.50 mm vs 40.61 ± 2.13 mm; P < 0.01) compared with fetuses in the usual-care group (n = 44). Fetuses in the stress-reduction group (n = 44) also had a deeper left insula (mean ± SD, 28.39 ± 1.13 mm vs 27.49 ± 1.26 mm; P = 0.04) compared with those in the usual-care group. CONCLUSION: Structured maternal lifestyle interventions during pregnancy may influence fetal neurodevelopment. Although the effect sizes were submillimetric, these effects were detectable using two-dimensional MRI, which highlights its potential as a sensitive tool for detecting subtle brain changes during fetal life. Future studies are warranted to truly reveal the clinical meaning of these findings. © 2026 International Society of Ultrasound in Obstetrics and Gynecology.