Developmental scores at 1 year with increasing gestational age, 37-41 weeks.

OBJECTIVE To examine the relationship between gestational age and mental and psychomotor development scores in healthy infants born between 37 and 41 weeks. METHODS The cohort included 1562 participants enrolled during infancy in an iron deficiency anemia preventive trial in Santiago, Chile. All participants were healthy, full-term (37-41 weeks) infants who weighed 3 kg or more at birth. Development at 12 months was assessed using the Bayley Scales of Infant Development. Using generalized linear modeling, we analyzed the association between gestational age and 1-year-old developmental status, taking into account potential confounders including birth weight percentile, gender, socioeconomic status, the home environment, iron status, and iron supplementation. RESULTS For each additional week of gestation, the Mental Development Index increased by 0.8 points (95% confidence interval = 0.2-1.4), and the Psychomotor Development Index increased by 1.4 points (95% confidence interval = 0.6-2.1) controlling for birth weight percentile, gender, socioeconomic status, and home environment. CONCLUSIONS In a large sample of healthy full-term infants, developmental scores obtained using the Bayley Scales of Infant Development at 12 months increased with gestational age (37-41 weeks). There is increasing evidence that birth at 39 to 41 weeks provides developmental advantages compared with birth at 37 to 38 weeks. Because cesarean deliveries and early-term inductions have increased to 40% of all births, consideration of ongoing brain development during the full-term period is an important medical and policy issue.