Late-Preterm Birth and Its Association With Cognitive and Socioemotional Outcomes at 6 Years of Age

The prevalence of late-preterm birth (defined as 34-36 weeks' gestation) has increased substantially in the last 2 decades and now accounts for more than 70% of all singleton preterm deliveries in the United States. Late preterm birth has been linked to lower educational attainment and income, and it is important to determine the relationship between late preterm birth and cognitive performance across childhood. Previous studies have demonstrated that late-preterm birth is associated with cognitive and socioemotional problems during childhood. However, many of these studies failed to include important contributors to cognitive and socioemotional outcomes such as maternal IQ. Moreover, it is known that reductions in fetal growth may also result in late-preterm delivery and it is unclear whether effects of preterm birth on cognitive and behavioral functioning are independent of changes in fetal growth. This study investigated whether infants born late preterm and children born term differed in IQ and teacher-reported behavioral problems at age 6 years. Data were obtained from a previous study investigating cognitive and psychiatric sequelae associated with low birth weight. The study population consisted of random samples of low-birth-weight (n = 473) and normal-birth-weight (n = 350) infants from urban and suburban hospitals. Singletons born late-preterm were matched 1: 1 with term counterparts using birth weight z scores within 0.1 SD of the counterpart value, yielding a total of 336 participants (168 pairs). Subsets of the age-norm Wechsler Intelligence Scale for Children-Revised measured a range of cognitive abilities, including full-scale IQ (FSIQ) and its constituent subscale, performance IQ (PIQ). To determine the effect of late preterm birth on cognitive and behavioral functioning at the age of 6 years, associations among late-preterm birth, IQ, and teacher-rated behavioral problems were investigated using random-effects models. After adjustment for confounders, late-preterm birth was associated with an increased risk of FSIQ and PIQ scores <85; the adjusted odds ratio (aOR) for the FSIQ score was 2.35, with a 95% confidence interval (CI) of 1.20-4.61 and the aOR for the PIQ score was 2.04, with a 95% CI of 1.09-3.82 (P <= 0.05 for both comparisons). With respect to behavioral problems, late-preterm birth was associated with an increased risk of exhibiting borderline or clinically significant internalizing problems (aOR, 2.35; 95% CI, 1.28-4.32) or attention problems (aOR, 1.76; 95% CI, 1.04-3.0) problems (P <= 0.05 for both comparisons). These findings show that children born late preterm exhibit higher levels of behavioral problems and lower levels of cognitive performance at the age of 6 compared with term counterparts, independent of socioeconomic factors and maternal IQ.