Functional brain development in growth‐restricted and constitutionally small fetuses: a fetal magnetoencephalography case–control study

Objective Fetal magnetoencephalography records fetal brain activity non‐invasively. Delayed brain responses were reported for fetuses weighing below the tenth percentile. To investigate whether this delay indicates delayed brain maturation resulting from placental insufficiency, this study distinguished two groups of fetuses below the tenth percentile: growth‐restricted fetuses with abnormal umbilical artery Doppler velocity (IUGR) and constitutionally small‐for‐gestational‐age fetuses with normal umbilical artery Doppler findings (SGA) were compared with fetuses of adequate weight for gestational age (AGA), matched for age and behavioural state. Design A case–control study of matched pairs. Setting Fetal magnetoencephalography‐Center at the University Hospital of Tuebingen. Population Fourteen IUGR fetuses and 23 SGA fetuses were matched for gestational age and fetal behavioural state with 37 healthy, normal‐sized fetuses. Methods A 156‐channel fetal magentoencephalography system was used to record fetal brain activity. Light flashes as visual stimulation were applied to the fetus. The Student's t‐test for paired groups was performed. Main outcome measure Latency of fetal visual evoked magnetic responses (VER). Results The IUGR fetuses showed delayed VERs compared with controls (IUGR, 233.1 ms; controls, 184.6 ms; P = 0.032). SGA fetuses had similar evoked response latencies compared with controls (SGA, 216.1 ms; controls, 219.9 ms; P = 0.828). Behavioural states were similarly distributed. Conclusion Visual evoked responses are delayed in IUGR fetuses, but not in SGA. Fetal behavioural state as an influencing factor of brain response latency was accounted for in the comparison. This reinforces that delayed brain maturation is the result of placental insufficiency.