Babies that have healthy growth before they're born, leading to higher birth weights, longer birth lengths and large head circumference within the normal range are more likely to have higher IQ scores.

Birth parameters have been hypothesised to have an influence on IQ. However, studies within the range of normal birth size have been sparse. To examine the associations between birth length, birth weight, head circumference, and gestational age within the normal birth size range in relation to childhood IQ in Asian children, researchers identified 2,913 Asian children aged 7 to 9 years, recruited from three schools in Singapore. Almost 2000 children were followed yearly from 1999 onward. Birth measurements were documented along with childhood IQ at ages 8 to 12 years. The average IQ score of the children was 114.2, with no significant difference between boys and girls.

It was found that for every 1-centimeter increase in birth length, 1-kilogram increase in birth weight, or 1 centimeter in head circumference, there was a corresponding increase in IQ of 0.49, 2.19, and 0.62 points, respectively.

Even small differences in birth parameters, within the normal birth size range, could be a sign of alterations in the fetal environment that affect its development.

The above finings indicate that longer birth length, higher birth weight, or larger head circumferences within the normal birth size range are associated with higher IQ scores in Asian children. The results also suggest that antenatal factors reflected in altered rates of growth, though within the normal range, could play a role in developing mental potential.