Poster #18 - Birthweight and IQ in Young Adulthood

• In Event: Poster Session 09

Abstract

Background: According to the Developmental Origins of Health and Disease (DOHaD) hypothesis, suboptimal prenatal conditions can permanently alter the expression of genes resulting in adverse effects on later health (Godfrey and Barker, 2000; Suzuki, 2018). Birthweight is considered a useful indicator for the quality of the prenatal environment and previous studies have found birthweight to be positively associated with intelligence (Shenkin, Starr and Deary, 2004; Grove et al. 2017). The anticipated biological pathway to explain this association is that exposed to a suboptimal prenatal environment, the developing brain will not receive the optimal amount of nutrients and oxygen in utero, which negatively influences the normal development of the brain and thus intelligence. Intelligence is of major importance for various health outcomes across the life course, why early predictors of intelligence is of interest in a prevention perspective. Previous studies have mainly been delimited to low birthweight, why research examining the full range of birthweight is warranted.

Aim: To examine the association between birthweight and intelligence among young Danish men born between 1980 and 2001 within the full range of birthweight.

Method: The study was conducted in a register-based design and comprised a population of Danish men that had completed the draft board examination between 1st of January 2006 and 31st of December 2019 (N=222,496). Based on data on birthweight from the Danish Birth Registry and intelligence test scores from the Danish Conscription Registry, the association between birthweight and intelligence was analyzed using general linear models. Significant interactions were found between birthweight and length of gestation and maternal level of education, respectively, and all analyses were stratified by these two variables.

Results: Across the six groups of maternal education (low, medium, high) and length of gestation (37-39 weeks, 40+ weeks), the results indicated a small to modest significant positive association between birthweight and intelligence. For instance, men with a birthweight of 3000-3499g, born of a mother with a medium level of education and a gestational age of 40+ weeks on average had -1.53 (CI-1.77; -1.28) (table 1) points lower IQ than men with a birthweight of 3500-3999g with the same level of maternal education and gestational age (adjusted for Apgar score, maternal age at birth, paternal age at birth, paternal level of education, birth order, birth year, conscription year). A longer period of gestation was associated with an increased magnitude and statistical strength of the association. Regarding maternal level of education, the magnitude and statistical strength of the association became higher the lower the level of maternal education (Figure 1).

Conclusion: The association between birthweight and intelligence was examined in a large representative population in a model adjusted for most of the suspected confounding variables. The results were stratified by length of gestation and maternal level of education due to significant interaction. The results provide evidence that the quality of the prenatal environment could play a part in the development of intelligence. This situates the prenatal period as a window for public health intervention.

Authors

• Emma Bro Hansen, University of Copenhagen

• Gunhild Tidemann Okholm, University of Copenhagen

• Frederik Palmgren Kjaer, University of Copenhagen

• Cathrine Lawaetz Wimmelmann, University of Copenhagen

• Merete Osler, Bispebjerg and Frederiksberg Hospitals

• Erik Lykke Mortensen, University of Copenhagen

• Trine Flensborg-Madsen, University of Copenhagen
  Presenting Author