Preterm Birth, Poor Fetal Growth Increase Risk for ADHD

Jennifer Garcia

August 24, 2015

According to a new population-based study, infants born prematurely or those who demonstrate poor fetal growth are at an increased risk of developing attention-deficit/hyperactivity disorder (ADHD), and this risk persists even among early term infants. The findings were published online August 24 in Pediatrics.

"We demonstrated that each declining week of gestation increased the risk of ADHD. This emphasizes the significance of each gestational week for later neurodevelopment," report Minna Sucksdorff, MD, from the University of Turku in Finland, and colleagues. "However, we also showed that poor fetal growth increased the risk of ADHD."

Researchers evaluated data from 10,321 patients with ADHD along with 38,355 age- and sex-matched control patients to determine the association between gestational age and weight and the risk of developing ADHD. The researchers also stratified a potential association by week of fetal maturity.

Data from Finnish nationwide registers and the Finnish Medical Birth Register were used to identify singleton infants born between January 1, 1991, and December 31, 2005, and diagnosed with ADHD until December 31, 2011. Children diagnosed with ADHD before 2 years of age, those with severe mental retardation, or those lacking information regarding gestational age or birth weight were excluded. The mean age of ADHD diagnosis was 7.6 years, and 84% of the children diagnosed were boys.

The researchers found that "[t]he risk of ADHD increased by each declining week of gestation," after adjusting for confounders such as smoking during pregnancy, parental age, socioeconomic status, and parental psychiatric history. The adjusted odds ratio (OR) at week 25 was 5.77 (95% confidence interval [CI], 1.68 - 19.83). At week 30, the OR was 3.55 (95% CI, 2.02 - 6.23), and by week 35, it was 1.41 (95% CI, 1.12 - 1.78). Further, the researchers noted a declining but persistent level of risk by week 37 (OR, 1.31; 95% CI, 1.16 - 1.47) and week 38 (OR, 1.12; 95% CI, 1.03 - 1.22).

In addition, the authors found an increased risk for ADHD among infants determined to be small for gestational age, noting that infants born more than two standard deviations below the mean gestational weight had almost double the risk of having a diagnosis of ADHD (OR, 1.80; 95% CI, 1.58 - 2.05) after adjusting for confounders. Similar results were found among infants born large for gestational age, with those more than two standard deviations having a 1.21-fold (95% CI, 1.05 - 1.40-fold) greater risk.

The researchers point out that although an association with ADHD and preterm birth has been evaluated in the past, it is worth noting that even late preterm infants (34 - 36 weeks), as well as early term infants (37 - 38 weeks) had a modest, but increased, risk of developing ADHD, which can translate to "a substantial number of ADHD cases at the population level."

Multiple factors may be at play, including disruption of cortical development and myelination, as well as factors that influence preterm labor such as infection, immune-mediated processes, or stress, the authors suggest.

They conclude that these findings highlight "the importance of taking into account both prematurity and poor fetal growth when planning follow-up and support policies."

Funding for this study was provided by the Sigrid Juselius Foundation and the Academy of Finland. The authors have disclosed no relevant financial relationships.

Pediatrics. Published online August 24, 2015. Abstract

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