Abstract
Multiple studies have reported that individuals with low birth weights (LBW, <2500 g) have a lower intelligence quotient (IQ) than those with normal birth weights (NBW, ≥2500 g). Based on 57 eligible individual studies including 12,137 participants, we performed a meta-analysis to estimate the association between low birth weight and individuals’ IQ scores (IQs). The pooled weight mean difference (WMD) in IQs between NBW and LBW individuals was 10 (95% CI 9.26–11.68). The WMD was stable regardless of age. No publication bias was detected. The mean IQs of the extremely low birth weight (ELBW, <1000 g), very low birth weight (VLBW, 1000–1499 g), moderately low birth weight (MLBW, 1500–2499 g) and NBW individuals were 91, 94, 99 and 104, respectively. Additionally, the WMD in IQs with NBW were 14, 10 and 7 for ELBW, VLBW, and MLBW individuals, respectively. Two studies permitted estimates of the influence of social determinants of health to the discrepancy in IQs, which was 13%. Since IQ is inherited and influenced by environmental factors, parental IQs and other factors contribute to residual confounding of the results. As the conclusion was based on population studies, it may not be applicable to a single individual.
Highlights
Infants with low birth weight (LBW), very low birth weight (VLBW) and extremely low birth weight (ELBW) are considered to be at a high risk of cognitive dysfunction1–3, such as attention deficit4,5, executive function issues6–8 and low average to borderline intelligence quotient (IQ)1,4,6–8
A recent meta-analysis containing 15 individual studies on the relationship between LBW and IQs in adolescent and early adulthood29 found that LBW individuals scored an average of 8 IQ points lower than normal birth weights (NBW) individuals
The results showed that the weight mean difference (WMD) between NBW and LBW individuals were and for social determinants between matched groups and non-matched groups (Figure S7), respectively
Summary
Infants with low birth weight (LBW), very low birth weight (VLBW) and extremely low birth weight (ELBW) are considered to be at a high risk of cognitive dysfunction, such as attention deficit, executive function issues and low average to borderline intelligence quotient (IQ). The effect of LBW accounted for a 0.4 standard deviation (SD) decrease in math and a 0.25 SD decrement in reading17 Those cognitive disadvantages would lead to low school achievements and persist into early adulthood, resulting in low socio-economic status (SES) in the future. The consistent finding was that LBW individuals had lower IQs than those with normal birth weights (NBW). A recent meta-analysis containing 15 individual studies on the relationship between LBW and IQs in adolescent and early adulthood (age ≥ 13) found that LBW individuals scored an average of 8 IQ points lower than NBW individuals. There have been more relevant studies focusing on preschool and school-aged children We integrated those studies into our meta-analysis to identify the age-related change in IQs between LBW and NBW individuals
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