Published online May 26, 2009
PEDIATRICS Vol. 123 No. 6 June 2009, pp. e1011-e1016 (doi:10.1542/peds.2008-3344)
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ARTICLE

The Influence of Birth Size on Intelligence in Healthy Children

Birit F. P. Broekman, MD, MAa, Yiong-Huak Chan, PhDb, Yap-Seng Chong, MRACOG, MDc, Swee-Chye Quek, MD, FRCPH, DCH, FACCd, Daniel Fung, MBBS, MMede,f, Yen-Ling Low, PhDg, Yoon-Phaik Ooi, PhDe, Peter D. Gluckman, DsC, FMedSci, FRSg,h, Michael J. Meaney, PhDi, Tien-Yin Wong, PhDj,k,l and Seang-Mei Saw, MBBD, PhDm

a Departments of Psychological Medicine
c Obstetrics and Gynecology
d Pediatrics
l Ophthalmology
m Community, Occupational, and Family Medicine
b Yong Loo Lin School of Medicine, National University of Singapore/National University Health System, Singapore
e Department of Child and Adolescent Psychiatry, Institute of Mental Health, Singapore
f Division of Psychology, School of Humanities and Social Sciences, Nanyang Technological University, Singapore
g Singapore Institute for Clinical Sciences, Singapore
h Liggins Institute, University of Auckland, Auckland, New Zealand
i Departments of Psychiatry and Neurology and Neurosurgery, Douglas Hospital Research Centre, McGill University, Montreal, Quebec, Canada
j Singapore Eye Research Institute, Singapore
k Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia

OBJECTIVE. Birth parameters have been hypothesized to have an influence on IQ. However, studies within the range of normal birth size have been sparse. With this study we examined 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.

METHODS. A cohort of 1979 of 2913 Asian children aged 7 to 9 years, recruited from 3 schools in Singapore, were followed yearly from 1999 onward. Birth parameters were recorded by health personnel. Childhood IQ was measured with the Raven's Standard Progressive Matrices at ages 8 to 12.

RESULTS. The mean IQ score across the sample (n = 1645) was 114.2. After controlling for multiple confounders for every 1-cm increment in birth length, 1 kg in birth weight, or 1 cm in head circumference, there was a corresponding increase in IQ of 0.49 points (P for trend < .001), 2.19 points (P for trend = .007) and .62 points (P for trend = .003), respectively. These associations persisted even after exclusion of premature children and children with extreme weights and head circumferences.

CONCLUSIONS. 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. Our results suggest that antenatal factors reflected in altered rates of growth but within the normative range of pregnancy experiences play a role in generating cognitive potential. This has implications for targeting early intervention and preventative programs.

Key Words: fetal growth • neurodevelopmental • birth weight • intelligence • gestational age

Abbreviations: BW—birth weight • BL—birth length • GA—gestational age • HC—head circumference • RPM—Raven's Standard Progressive Matrices • CI—confidence interval

Accepted Feb 12, 2009.


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