Low gestational age, weight associated with lower IQ scores into adulthood

Results of a meta-analysis demonstrated that lower gestational age and weight were important risk factors associated with lower IQ scores into adulthood, researchers reported in JAMA Pediatrics.

Robert Eves, MSc, a doctoral student in the department of psychology at Warwick University in the United Kingdom, and colleagues assessed the differences in adult IQ levels among people who were born very preterm (VPT; birth before 32 weeks’ gestation) or who had a very low birth weight (VLBW; birth weight less than 1,500 g) compared with term-born individuals.

Their data came from a systematic review of published data from PubMed and a meta-analysis of individual participant data from cohorts in the Research on European Children and Adults Born Preterm (RECAP) and Adults Born Preterm International Collaboration (APIC) consortia.

Participants were eligible for inclusion if they were born either VPT or VLBW and had completed a standardized IQ test at the mean age of 17 years or older. According to the study, all cohorts were required to include a control group of term-born participants in order to obtain comparable IQ scores.

Eves and colleagues identified 426 records, including 413 from PubMed and the remaining from either RECAP or APIC. However, 342 records were excluded based on titles and abstracts, and 84 articles remained.

The mean gestational age among those included in the study was 28.3 weeks. The mean age of participants when performing the IQ test was 24.4 years among VPT/VLBW participants and 24.8 years among term-born participants.

The mean IQ scores among VPT/VLBW participants were 0.78 SD (95% CI, –0.9 to –0.66) lower than those born at term. When including sex and maternal education into the analysis, the difference was minimally reduced from 0.78 to 0.74 SD (95% CI, –0.85 to –0.63). When excluding those with neurosensory impairment, the IQ difference decreased from 0.78 to 0.65 SD (95% CI, –0.76 to –0.55).

According to the authors, significant associations with IQ scores in the multivariable analysis included gestational age (score difference per week of gestation, 0.11; 95% CI, 0.07-0.14), birth weight score (difference, 0.21; 95% CI, 0.14-0.28), the presence of neonatal bronchopulmonary dysplasia (difference, –0.16; 95% CI, –0.3 to –0.02), any grade of intraventricular hemorrhage (difference, –0.19; 95% CI, –0.33 to –0.05) and maternal education level (difference, 0.26; 95% CI, 0.17-0.35).

“These findings indicated, for example, that among VPT/VLBW participants, each extra week of gestation was associated with an increase in IQ z score of 0.11, which was equivalent to 1.65 IQ points,” the authors wrote.