BACKGROUND: Some studies have indicated an increased risk of attention deficit hyperactivity disorder (ADHD) and a small, sex-specific association with autism spectrum disorder (ASD) among children prenatally exposed to obstetric oxytocin. Since oxytocin is widely used in the obstetric ward, these potentially deleterious effects are of concern. Thus, we aimed to examine whether obstetric oxytocin treatment for labour induction or augmentation is associated with ADHD and ASD in offspring born in a two-country design based on data from Denmark and Finland.

METHODS: This population-based study used data from national registers in Denmark and Finland. Singletons born in Denmark 2000-10 (n = 577 380) and Finland 1991-2010 (n = 945 543), who survived infancy, were followed until 31 December 2015. ADHD and ASD were defined using diagnostic codes. For ADHD, we also included information on prescribed and redeemed ADHD medication in the definition. Hazards ratios (HRs) with 95% confidence intervals (CI), modelled with age as the underlying time scale, were calculated to estimate the associations.

RESULTS: Oxytocin was used in 31% and 46% of the included deliveries in Denmark and Finland, respectively. In crude analyses, prenatal oxytocin was associated with an approximately 20% increased risk of ADHD and ASD, but confounder adjustment attenuated the association. The adjusted HR was 1.03, 95% CI 1.01-1.05, for ADHD and 1.05, 95% CI 1.02-1.08, for ASD. The results were similar in across country and gender.

CONCLUSIONS: We found an association between synthetic oxytocin and ADHD or ASD which is unlikely to reflect a causal association and thus should not support the concern of clinical use. Our results help to allay concerns of obstetric use of oxytocin causing ADHD or ASD.