Impairment of the frontal lobe in late-onset fetal growth restriction: is it detectable in fetuses with a normal cerebroplacental ratio?

In fetal growth restriction (FGR), the brain-sparing effect refers to a hemodynamic adaptation that prioritizes blood flow to the brain. The aim of this study was to assess whether fetuses with late-onset FGR have smaller brain structures and evaluate whether the structural impairments of the brain are present even when the cerebroplacental ratio (CPR) is still normal. In this prospective cross-sectional study, ultrasonography was used to measure the frontal antero-posterior diameter (FAPD), occipito-frontal diameter (OFD), biparietal diameter (BPD), sylvian fissure depth (SFD), and insular lobe depth (ILD) in 30 control fetuses and 90 late-onset small fetuses: 30 small for gestational age (SGA) and 60 FGR. The FAPD/OFD, SFD/BPD and ILD/BPD ratios were calculated. The differences in FAPD, ILD, SFD, and their ratios among the study groups were calculated. Compared to controls or SGA, late-onset FGR fetuses had significantly smaller FAPD (both P < 0.01)and FAPD/OFD ratio ((both P < 0.05)), but there were no differences in FGR between normal and abnormal CPR (P > 0.05). Frontal lobe changes were present in 56.7% (34/60) of all FGR fetuses. In addition, FGR with abnormal CPR was associated with smaller head circumference and OFD relative to controls (P < 0.05). No significant differences were found in ILD, SFD, SF/BPD ratio, or IL/BPD ratio among the four groups (P > 0.05). Ultrasound may be a sensitive and convenient method of detecting changes in the brain in late-onset FGR. Frontal lobe impairment was observed in late-onset FGR fetuses regardless of their CPR status, suggesting that this structural change may be present even in those with a normal CPR.