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Very preterm or very low birthweight associated with lower IQ into adulthood

The average IQ of adults who were born very preterm (VP) or at a very low birth weight (VLBW), compared to adults born full term, is associated with continued lower IQ performance into adulthood, found a University of Warwick study.

VP/VLBW children may require special support in their education to boost their learning throughout childhood, the study in JAMA Pediatrics notes.

Birth before 32 weeks of gestation is classed as very preterm (VP) and those born weighing less than 1500g are classed as very low birthweight (VLBW). Research has previously found that those who were born VP or VLBW had lower cognitive performance in childhood.

Participants were 1068 VP/VLBW adults and 1067 term born controls born between 1978-1995 from 6 cohort studies in Europe and 2 from Australia and New Zealand, who had been studied from birth and had their IQ assessed in adulthood (aged 18-30 years).

The average IQ score in the general population is 100. The researchers found that VP/VLBW individuals scored approximately 12 IQ points less (i.e. 88) compared to term born adults (born 37-41 weeks gestation). Even when they removed those who had a childhood neurosensory impairment or learning disability (e.g childhood IQ score below 70) the adult IQ difference between VP/VLBW and term born adults was still on average 9.8 IQ points.

The risk factors that were associated with lower IQ performance for VP/VLBW adults included neonatal severe lung problems (bronchopulmonary dysplasia), neonatal bleeds into their brain (intraventricular haemorrhage) and being born to mothers with lower education.

Robert Eves, first author from the Department of Psychology at the University of Warwick comments:

"We have found that being born very preterm or at a very low birthweight continues to have a highly significant long term impact on the average IQ as compared to their peers in 7 different countries. The multi cohort, international aspect of this research can especially give us confidence in this important finding"

Professor Dieter Wolke, senior author and project lead from the Department of Psychology at the University of Warwick adds: "While most born VP/VLBW show cognitive development within the normal range, many may benefit from better tailored early interventions. These may include reducing bronchopulmonary dysplasia and intraventricular haemorrhage in neonatal care and educational interventions of those born into socially disadvantaged families."

Study details

Association of Very Preterm Birth or Very Low Birth Weight With Intelligence in Adulthood
An Individual Participant Data Meta-analysis

Authors: Robert Eves, Marina Mendonça, Nicole Baumann, Yanyan Ni, Brian A. Darlow, John Horwood, Lianne J. Woodward, Lex W. Doyle, Jeanie Cheong, Peter J. Anderson, Peter Bartmann, Neil Marlow, Samantha Johnson, Eero Kajantie, Petteri Hovi, Chiara Nosarti, Marit S. Indredavik, Kari-Anne I. Evensen, Katri Räikkönen, Kati Heinonen, Jennifer Zeitlin, Dieter Wolke.

Published in JAMA Pediatrics on 31 May 2021

Key Points

Question Is very preterm birth or very low birth weight vs term birth associated with intelligence in adulthood?

Findings In this meta-analysis of individual participant data from 8 cohorts comprising 2135 adults with and without very preterm birth or very low birth weight in 7 countries, IQ was significantly lower among adults who were born very preterm or with very low birth weight compared with adults who were born at term, with a mean between-group difference of approximately 12 IQ points. Lower gestational age, lower birth weight z scores, the presence of neonatal bronchopulmonary dysplasia or intraventricular hemorrhage, and lower maternal educational levels were significantly associated with lower IQ among adults born very preterm or with very low birth weight.

Meaning This individual patient data meta-analysis suggests that very preterm birth or very low birth weight may be associated with a clinically relevant difference in IQ, relative to term birth, in adulthood.

Abstract

Importance Birth before 32 weeks’ gestation (very preterm [VPT]) and birth weight below 1500 g (very low birth weight [VLBW]) have been associated with lower cognitive performance in childhood. However, there are few investigations of the association of neonatal morbidities and maternal educational levels with the adult cognitive performance of individuals born VPT or VLBW (VPT/VLBW).

Objective To assess differences in adult IQ between VPT/VLBW and term-born individuals and to examine the association of adult IQ with cohort factors, neonatal morbidities, and maternal educational level among VPT/VLBW participants.

Data Sources Systematic review of published data from PubMed and meta-analysis of individual participant data (IPD) of cohorts from 2 consortia (Research on European Children and Adults Born Preterm [RECAP] and Adults Born Preterm International Collaboration [APIC]).

Study Selection The meta-analysis included prospective longitudinal cohort studies that assessed the full-scale IQ of adults born VPT or VLBW and respective control groups comprising term-born adults.

Data Extraction and Synthesis The study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline for analyses of individual participant data and identified 8 studies that provided data from 2135 adults (1068 VPT/VLBW and 1067 term-born participants) born between 1978 and 1995. Meta-analyses of IPD were performed using a 1-stage approach, treating VPT birth or VLBW and cohort as random effects.

Main Outcomes and Measures Full-scale IQ scores were converted to z scores within each cohort using the combined SD of VPT/VLBW participants and a control group of term-born participants, with scores centered on the mean of the control group.

Results A total of 426 records were identified and screened. After exclusions, 13 studies were included in the aggregate meta-analysis. The IPD meta-analysis included 8 of the 9 RECAP and APIC cohorts with adult IQ data. The mean (SD) age among the 8 IPD cohorts was 24.6 (4.3) years, and 1163 participants (54.5%) were women. In 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 participants, equivalent to a difference of 12 IQ points. Among VPT/VLBW participants, 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 bronchopulmonary dysplasia (score difference, −0.16; 95% CI, −0.30 to −0.02) or any grade of intraventricular hemorrhage (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) were all significantly associated with lower IQ scores in adulthood.

Conclusions and Relevance In this IPD meta-analysis, lower gestational age, lower weight for gestational age, neonatal morbidities, and lower maternal educational levels were all important risk factors associated with lower IQ among young adults born VPT or VLBW.

 

Full study in JAMA Pediatric (Open access)

 

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