To assess the stability of developmental problems in moderately-late preterm-born children compared with early preterm and full term-born children before school entry at age 4 years and 1 year after school entry at age 5 years.

We included 376 early preterm, 688 born moderately-late preterm, and 403 full term-born children from the Longitudinal Preterm Outcome Project (LOLLIPOP) cohort study. Developmental problems were assessed by the total score and the 5 domain scores of the Ages and Stages Questionnaire at ages 4 (ASQ-4) and 5 (ASQ-5). From the combinations of normal and abnormal ASQ-4 and ASQ-5 scores we constructed 4 categories: consistently normal, emerging, resolving, and persistent problems.

The ASQ-4 total score was abnormal more frequently in moderately-late preterm (7.9%, P = .016) and early preterm-born children (13.0%, P < .001) than in full term-born children (4.1%). Compared with the ASQ-5 total score, moderately-late preterm-born children had persistence and change comparable with full term-born children, and early preterm-born children had significantly greater rates than full term-born children of persistent (8.4% vs 2.2%, P < .001) and emerging problems (7.8% vs 2.7% P = .001). On the underlying domains, both early preterm and moderately-late preterm-born children had mainly emerging motor problems and resolving communication problems, but the changing rates of moderately-late preterm-born children were lower.

After school entry, the overall development of moderately-late preterm-born children had stability patterns comparable with full term-born children, whereas early preterm-born children had greater rates of persistent and emerging problems. On the underlying domains, moderately-late preterm-born children had patterns comparable with early preterm-born children but at lower rates.