1. Intelligence Quotient (IQ) was significantly lower among adults born very preterm or with very low birth weight compared to adults born at term.
2. Lower gestational age, lower birth weight, the presence of neonatal morbidities, and lower maternal educational levels were all significantly associated with lower IQ among adults born very preterm or with very low birth weight.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Birth prior to 32 weeks’ gestation, referred to as very preterm (VPT), and birth weight below 1,500 g, referred to as very low birth weight (VLBW) have been associated with lower cognitive performances in childhood. However, few studies have investigated the association of neonatal morbidities and potential risk factors such as maternal educational levels with adult cognitive performances in individuals born VPT or VLBW (VPT/VLBW). In order to meet this demand, the authors of this study performed a meta-analysis of individual participant data (IPD) of Intelligent Quotient (IQ) in adulthood with three primary objectives. The first was to compare the difference in adult IQ between VPT/VLBW participants and a control group of term-born participants. The second was to examine cohort and individual-level risk factors associated with adult IQ among VPT/VLBW participants. The third was to conduct a sensitivity analysis assessing whether adult IQ scores from the IPD cohorts were representative of all cohorts of VPT/VLBW individuals. In this IPD meta-analysis, full-scale IQ scores were converted to z scores within each cohort using the combined standard deviation of VPT/VLBW participants and a control group of term-born participants, with scores centered on the mean of the control group. In total, data from 8 cohorts comprising 2,135 adults with and without VPT/VLBW found that IQ scores were significantly lower among adults who were born VPT/VLBW compared with adults who were born at term, with a mean between-group difference of approximately 12 IQ points. Furthermore, lower gestational age, lower birth weight z scores, the presence of neonatal bronchopulmonary dysplasia (BPD) or intraventricular hemorrhage (IVH), and lower maternal educational levels were significantly associated with lower IQ among adults born very preterm or with very low birth weight. One limitation of this study was the variability in cohorts with regards to eligibility criteria, including the stricter inclusion criterion of less than 26 weeks’ gestational age in some studies, the use of maternal educational level rather than broader factors (e.g., socioeconomic status or combined parental educational level), and the different methods used for recruiting participants for the control groups.
In-Depth [systematic review and meta-analysis]: This meta-analysis included prospective longitudinal cohort studies that assessed the full-scale IQ of adults born VPT/VLBW and respective control groups comprising term-born adults. Systematic review of published data from PubMed and meta-analysis of IPD of cohorts from two consortia (Research on European Children and Adults Born Preterm [RECAP] and Adults Born Preterm International Collaboration [APIC]) were also used as data sources in the analysis. The study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline for analyses of IPD and identified 8 studies that provided data from 2,135 adults (1,068 VPT/VLBW and 1,067 term-born participants) born between 1978 and 1995 from 7 countries. Meta-analyses of IPD were performed using a one-stage approach, treating VPT birth or VLBW and cohort as random effects. In total, 426 records were screened using inclusion/exclusion criteria, after which 13 studies were included in the aggregate IPD meta-analysis. The mean (SD) age among the 8 IPD cohorts was 24.6 (4.3) years, and 1,163 participants (54.5%) were female. In the unadjusted analyses, VPT/VLBW participants had mean adult IQ scores that were 0.78 SD (95%CI, −0.90 to −0.66 SD) lower than term-born controls, equivalent to a difference of approximately 12 IQ points. Additionally, lower gestational age (score difference per week of gestation, 0.11; 95%CI, 0.07-0.14), lower birth weight z scores (score difference per 1.0 SD, 0.21; 95%CI, 0.14-0.28), the presence of neonatal BPD (score difference, −0.16; 95%CI, −0.30 to −0.02) or any grade of IVH (score difference, −0.19; 95%CI, −0.33 to −0.05), and lower maternal educational level (score difference, 0.26; 95% CI, 0.17-0.35) among VPT/VLBW cohorts were all significantly associated with lower IQ scores in adulthood.
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