Birth order, stimulating environment, and maternal factors in developmental outcomes: A longitudinal Mexican study.

This study longitudinally examined the interplay between birth-order and well-known risk factors in impoverished environments such as inadequate environmental stimulation, low maternal education, and young maternal age in children from birth to 36 months. In the developmental motor domain, the effect of the stimulating environment over time, favored first-borns. In the adaptive domain, maternal education privileged first-born boys. In language development, first-borns reached higher scores over time than laterborn identifying a positive impact of stimulation. In the personal-social domain, firstborns obtained higher averages overall, but stratified models revealed that later-borns reached the first-borns scores as maternal age increased.