Objective To characterise fetal brain growth in children with specific language impairment (SLI).

Design A nested case–control study.

Setting Perth, Western Australia.

Participants Thirty children meeting criteria for SLI at age 10 years were individually matched with a typically developing comparison child on sex, non-verbal ability, fetal gestational age, maternal age at conception, smoking and alcohol intake during pregnancy.

Main outcome measures Occipitofrontal head circumference (HC) was measured using ultrasonography at approximately 18 weeks gestation. Femur length provided a measure of fetal length. Occipitofrontal HC was measured at birth and at the 1-year postnatal follow-up using a precise paper tape measure, while crown-heel length acted as an index of body length at both time points. Raw data were transformed to z-scores using reference norms.

Results The SLI group had a significantly smaller mean HC than the typically developing comparison children at birth, but there was no group difference at 18 weeks gestation or at the 1-year postnatal follow-up. Individual analyses found that 12 SLI children had an HC z-score less than −1 at birth, with three of these cases meeting criteria for microcephaly. There was no group difference in the indices of overall body size at any time point.

Conclusions Children with SLI are more likely to have a small HC at birth but not at 18 weeks gestation or infancy, suggesting growth asynchrony in brain development during the second half of pregnancy.