Cognitive performance in childhood can be negatively impacted if an infant was Small for Gestational Age (SGA, birthweight <10% for gestation). As existing research did not show coinciding results on whether lower IQ scores continue to be present in adulthood, Eves et al. conducted an observational study to assess differences in IQ scores between SGA adults and Appropriate for Gestational Age (AGA) adults.

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The study compared the impact of low familial socioeconomic status and quality of parent-infant relationships on cognitive performance of SGA and AGA individuals. Furthermore, SGA effects on individuals born very preterm (VP) or with very low birth weight (VLBW) were assessed to determine possible differences.

414 individuals of which 197 were term-born and 217 were born VP or born with VLBW were included in the research. To determine cognitive performance, developmental tests and IQ tests were carried out 6 times at the ages of 5 months, 20 months, 4, 6, 8 and 26 years.

Socioeconomic status of parents was assessed within the first 10 days after the baby’s’ birth through educational qualification of both parents and the job of the highest earner. The parent-infant relationship was determined in the neonatal ward or 5 months after the baby’s’ birth through an interview with the parents.

The categorisation of individuals into the Small for Gestational Age group was difficult due to differing existing assessment schemes. One of these assessment schemes classified 28% of the VP/VLBW participants and 7% of the term-born individuals as SGA. The other assessment scheme classified 53% of the VP/VLBW participants and 11% of the term-born individuals as SGA. Therefore, the researchers of this study used both categorisations to perform their analysis and compared the results.

The results showed that regardless of the assessment scheme used for the categorisation of participants into the SGA group, SGA individuals showed lower IQ scores that can still be identified in adulthood. However, the difference in IQ scores between AGA and SGA participants decreased from about 8 IQ points at a young age to 2.01 or 3.78 IQ points (depending on the SGA assessment scheme) until individuals reached adulthood.

Furthermore, low familial socioeconomic status and a bad parent-infant relationship are significant risk factors for lower IQ scores during development with an even bigger impact than SGA. Low familial socioeconomic status had an impact on IQ (14 points lower) compared to individuals with a high socioeconomic status. Poor parent-infant relationship also showed a slightly bigger negative effect on IQ scores than SGA.

A limitation of the study is the small number of participants who were born moderately/late preterm or both SGA and term-born, which did not allow for a more detailed comparison regarding the impact of SGA on preterm born and VP/VLBW individuals.

Further research should be done to gain more knowledge about the effects of SGA on IQ scores and the possible impact of SGA on preterm born or VP/VLBW individuals.

Paper available to view at https://bit.ly/3j8PtjE

Full list of authors: Robert Eves, Marina Mendonça, Peter Bartmann, Dieter Wolke

DOI: 10.1111/1471-0528.16341