We are all aware of the potential harm that opioids can do to early brain development of infants born to addicted. Is there an association with infant brain size, as measured by head circumference? Towers et al. (10.1542/peds.2018-0541) decided to investigate this question by conducting a prospective cohort study from 2014 to 2016 comparing head circumferences of infants >34 weeks gestation with non-opioid exposed babies matched for race, parity, type of delivery, and gestational age. The outcome was the proportion of infants with head circumferences ≤10th percentile. 858 infants were enrolled (429 with neonatal abstinence syndrome (NAS) and 372 of these on opioid medication assisted treatment) and 429 controls). Mean head circumference for babies with NAS was 33.04 cm compared to 33.99 cms for controls and 30.1% of those with NAS had a HC < 10th percentile and 8.2% had a circumference < 3rd percentile. When the authors adjusted for possible confounders including other co-morbidities and substances used by these mothers, they still found that chronic opioid use by the mothers during gestation was the key risk factor for the observed smaller head circumference.
So what do the results of this study indicate in terms of brain development and other developmental issues? We asked Drs. Mark Hudak and Kartikeya Makker with expertise in the care for infants born to opioid-addicted mothers to share their thoughts about this study in an accompanying commentary (10.1542/peds.2018-3376). Drs. Hudak and Makker point out that there were proportionately greater decreases in head circumference than in birth weight in the NAS babies—suggesting that opioids are having a direct effect on head growth and in turn brain growth. They cite other studies suggesting that smaller head circumference at birth is associated with poorer school performance and lower adult occupational achievements as adults, although alcohol was usually the factor in those other studies and not opioids. And even if opioids are affecting the developing brain, is there a critical period when the brain is most affected by these drugs and is the dose or duration of exposure during pregnancy worth factoring into the brain development equation as well? There are some great hypotheses suggested in this commentary that are ripe for future prospective long-term studies including the cohort reported in the Towers et al. study—so stay ahead and check out both this fascinating study and commentary to learn more.