Defining Very Preterm Populations for Systematic Reviews With Meta-analyses

JAMA Pediatr. 2020;174(10):997-999. doi:10.1001/jamapediatrics.2020.0956

Research Letter

Survival of very preterm (VPT) infants (ie, those born at <32 weeks’ gestation) has improved markedly over recent decades, raising concerns about levels of impairment among survivors. Numerous studies have been conducted on the association between VPT birth and long-term neurodevelopment and health, and this voluminous literature is increasingly synthesized in systematic reviews with meta-analyses. This methodology is considered to provide the highest level of evidence, but its validity depends on appropriate selection of primary studies and management of heterogeneity. Heterogeneity is pervasive in the literature about VPT birth because of differences in criteria for defining preterm populations, study designs, follow-up periods, follow-up rates, and clinical assessments. Furthermore, medical practices, survival, and morbidities vary markedly across countries and hospitals and can affect long-term prognosis. This study aimed to compare the selection criteria, findings, and heterogeneity of systematic reviews with meta-analyses of cognitive outcomes after VPT birth, which are of major concern in this population and measured in most studies.


We searched for systematic reviews with meta-analyses published between January 2000 and August 2019 that were based on observational studies with cohort designs investigating general cognition (IQ) for VPT children compared with a control group. We defined search terms to identify studies (1) on preterm birth (premature OR preterm OR infant, Premature [Medical Subject Headings (MeSH)]), (2) the outcome [Developmental disabilities [MeSH] OR cognition disorders [MeSH] OR intellectual disability [MeSH] OR cognition [MeSH] OR cognit* OR intelligence OR IQ, and (3) the type of study (Meta-analysis OR meta analys* OR metaanaly* OR [systematic AND review* OR overview*] OR Review Literature as Topic [MeSH]). Two of us (M.S. and J.Z.) independently abstracted methods and results related to study selection, pooled analyses, and heterogeneity. We compiled primary studies and identified unique cohorts when several studies originated from the same cohort based on the country, birth year(s), and research group. For analyses, we used R statistical software, version 3.5.0 (The R Foundation).


Five reviews were identified: 1 was published in 20121 and 4 were published in 2018 or 2019.25 All investigated the association of birth at less than 32 weeks’ gestation with childhood IQ, although some also considered other outcomes or subgroups. Eligibility criteria varied for birth weight, assessment ages, and study period (Table). We searched MEDLINE,15 Embase,1,2 PsychInfo,1,35 and Web of Science3,4 using different search terms.