Objectives: (1) To compare the mental and psychomotor development of low birth weight term (LBW-T) infants with that of appropriate birth weight (ABW) infants at 6 and 12 months of age. (2) To examine the relationship between developmental levels and social background.
Methods: A cohort of 131 LBW-T infants (1500 to 2499 gm) and 131 ABW infants (3000 to 3499 gm) matched for sex and time of birth, recruited from six maternity centers in Northeast Brazil were followed for 1 year. Their development was assessed with the Bayley Scales at 6 and 12 months of age, and at 12 months their behavior during the test was rated on five scales. Details of their families' socioeconomic status were recorded and the degree of stimulation in their homes was assessed.
Results: At 6 months of age the LBW-T infants had significantly lower scores than the ABW infants on the mental development index (MDI; 4.2 points lower, p < 0.001) and on the psychomotor development index (PDI; 7.3 points lower, p < 0.001). The difference had increased by 12 months of age (MDI 7.0 points lower, p < 0.001; PDI 9.9 points lower, p < 0.001). Socioeconomic variables were related to development at both ages in both groups. Maternal literacy was significantly related to the PDI in LBW-T infants at 12 months but not in ABW infants. Similarly, stimulation in the home was related to the MDI in LBW-T infants at 6 and 12 months but not in ABW infants. LBW-T infants were less active, cooperative, vocal, and happy, and were more inhibited than ABW infants.
Conclusions: LBW-T infants had poorer development than ABW infants and differed in their behavior. There was an interaction between birth weight and the environment. LBW-T infants, but not ABW infants, were affected by the quality of stimulation in the home and maternal illiteracy.