There is an increasing number of children with in utero exposure to opioids. Knowledge about opioid safety in pregnancy, particularly for outcomes later in childhood is scarce. It has been suggested that opioids can modulate immune system and increase the risk of infections. Our goal was to study the impact of in utero opioid exposure on the immune system and the risk of infections in childhood.
This population-based cohort study used nationwide registers from Denmark, Norway, and Sweden. Among pregnant women we identified users of opioids for two different indications, opioids used in opioid maintenance therapy (OMT) and opioids used for treatment of pain. We followed the exposed children and studied susceptibility for infections measured as number of antibiotic prescriptions expressed as Incidence rate ratios (IRRs) and diagnoses in specialist health care expressed as hazard ratios (HRs).
After adjustment we did not observe increased risk for filling antibiotic prescriptions in children exposed to OMT opioids compared with OMT discontinuers (IRR, 1.08; 95% CI 0.81-1.44 in Norway and Sweden, and IRR, 0.74; 95% CI 0.63-0.88 in Denmark), or for diagnosis of infection in specialist health care (HR 0.83; 95% CI 0.55-1.26 in Norway and Sweden, and 0.82; 95% CI 0.62-1.10 in Denmark).
In this population-based cohort study, we did not observe increased risk of infections among children prenatally exposed to OMT opioids when compared to OMT discontinuers, nor long-term analgesic opioids exposed when compared to short-term analgesic opioids exposed.

© 2020 John Wiley & Sons Ltd.