Fetal brain scans can predict a toddler’s vocabulary size years before they learn to speak

The size of a language-related brain region measured before a baby is born is linked to how many words that child can say at two to three years of age, according to a new study published in Developmental Science.

Children’s ability to learn and use words begins well before they say their first one. The brain regions most important for understanding and producing language—the superior temporal gyrus and the inferior frontal gyrus—begin taking shape around 24 to 25 weeks into a pregnancy, and are already partially formed during the third trimester.

After birth, the size and structure of these regions have been linked to language skills in both children and adults. However, whether the size of these same regions before birth can predict how well a child will develop language skills in the years after has rarely been directly tested.

Led by Annika Werwach of the Max Planck Institute for Human Development in Germany, the team used brain scans obtained from fetuses during the 30th to 33rd week of pregnancy as part of the Cambridge Human Imaging and Longitudinal Development (CHILD) project.

Forty-one fetuses had usable brain scans, and language abilities were later assessed via a parent-reported checklist of words their child could say at 18 months (25 children; 11 girls) and again at around 24 to 36 months (24 children; 13 girls). The average age of children at the later assessment was approximately 139 weeks, or roughly two years and eight months.

At the 18-month time point, Werwach’s team found no significant associations between prenatal brain size in either region and how many words children could say. However, by the 24-to-36-month assessment, a clear pattern emerged: children who had larger volumes in the superior temporal gyrus—the region most directly involved in processing sounds and words—before birth went on to produce significantly more words as toddlers.

Crucially, this association was found in both the left and right sides of the brain, not just the left side where language is typically concentrated in adults. This is consistent with the fact that young children rely on both sides of the brain for early language processing.

The inferior frontal gyrus—a region more involved in higher-level language functions like grammar and sentence structure—did not significantly predict early vocabulary.

The authors concluded: “This study shows that not only postnatal, but also prenatal volume in language-related brain regions is linked to language development years later. These findings suggest continuity between prenatal and postnatal neural networks regarding language development.”

However, the study comes with some caveats. The final sample size was very small (roughly two dozen children in the final analyses), and the participants came from predominantly white, middle-to-high-income families, meaning the findings need to be validated in larger, more diverse groups. Furthermore, the study only examined one aspect of language development—expressive vocabulary, meaning words a child can say—and did not assess receptive vocabulary (words a child understands) or other language skills.

The study, “Prenatal Volume in the Bilateral Superior Temporal Gyrus Associates With Children’s Expressive Vocabulary at 24–36 Months,” was authored by Annika Werwach, Alex Tsompanidis, Luca Villa, Roger Tait, John Suckling, Topun Austin, Sarah Hampton, Carrie Allison, Rosemary Holt, Simon Baron-Cohen, and Gesa Schaadt.