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.