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Biology versus environment in low birth weight children.

OBJECTIVE
To explore the contribution of biologic risk factors versus socio-demographic and environmental risk factors in cognitive development of children with birth weight less than 2000 g, at the age of 12 years.


DESIGN
Prospective cohort study.


SETTING
Infants discharged from a NICU of a referral hospital, with birth weight less than 2000 g between 1987-89 and followed up in the High Risk Clinic.


METHODS
The children were assessed at the age of 12 years, with the Weschler's Intelligence Scale for IQ and by Wide Range Achievement Test for mathematics skills. Mother's education, father's education, socio-economic status, family structure, spaciousness of the house, the locality in which the child lived and the type of school the child attended, were all recorded. A stimulation score was determined at 6 and 12 months and 3 years. Family environment score was used at 12 years.


RESULTS
The cohort consisted of 180 children, with 90 controls. The mean IQ of the study group was 89.5 +- 16.9, which was significantly lower than that of controls (97.2 +- 14.1) (P < 0.05). The mathematical skills of the study group were significantly poorer (P < 0.05) than that of controls. A multiple linear regression analysis was done using IQ as the dependent variable and all risk factors at birth, stimulation scores and socio-environmental factors as independent variables. Mothers education was the most important factor contributing to the total IQ, a variance of 25.2 % of the total variance 44.2 PERCENT. Fathers education emerged as an important factor for mathematics skills. School was the next important factor for IQ as well as academics. Controlling for all other background factors, birth weight was the only biologic factor of significance, and this had a very small contribution.


CONCLUSION
Parental education and the type of school attended by the child were the most important factors influencing cognitive development. The only biologic factor of importance was birth weight, but this too had a very small contribution.