Incidence, antibiotic treatment and outcomes of lactational mastitis: Findings from The Norwegian Mother, Father and Child Cohort Study (MoBa)

Background: Mastitis is a common and distressing maternal postpartum condition, but the relationship between mastitis timing and antibiotic treatment and breastfeeding outcomes and postnatal mental health is unclear. Objectives: To describe the incidence of mastitis and treatment with antibiotics in first 6 months postpartum, and to investigate the impact of mastitis timing and antibiotic treatment on breastfeeding practices and postnatal mental health. Methods: This study is based on 79,985 mother-infant dyads in the Norwegian Mother, Father and Child Cohort Study (MoBa). Women were classified according to self-reported mastitis within first month (‘early’) or 1–6 months (‘later’) postpartum and antibiotic treatment. Breastfeeding outcomes included predominant or any breastfeeding and abrupt breastfeeding cessation until 6 months postpartum. Maternal mental health was assessed by self-report at 6 months postpartum. Results: The incidence of mastitis was 18.8%, with 36.8% reporting treatment with antibiotics. Women reporting early mastitis were less likely to report predominant breastfeeding (adjustedd relative risk [aRR] 0.92, 95% confidence interval [CI] 0.86, 0.99) and any breastfeeding for 6 months (aRR 0.97, 95% CI 0.96, 0.98) than women who did not report mastitis, and more likely to report abrupt breastfeeding cessation (aRR 1.37, 95% CI 1.23, 1.53). Late-onset mastitis was not associated with poorer breastfeeding outcomes. Among women reporting mastitis, the risk of abrupt breastfeeding cessation was higher in those also reporting antibiotic use. Mastitis was associated with an increased risk of mental health problems postpartum which was highest among those reporting no antibiotic use (aRR 1.29, 95% CI 1.18, 1.41), in contrast to those also reporting antibiotic use (aRR 1.08, 95% CI 0.96, 1.22). Conclusions: Lactational mastitis and its associated treatment with antibiotics are common. Early (<1 month postpartum) mastitis appears to be a modest risk factor for suboptimal breastfeeding outcomes. In addition, mastitis is associated with poorer mental health.