Objectives To assess implications for health care resources of infants born to drug misusing women and investigate factors associated with the development of neonatal abstinence syndrome (NAS).

Methods Retrospective cohort study 1/1/04 to 31/12/06.

Results 478 infants were born to 476 women, 96% of whom were prescribed substitute methadone in pregnancy. Despite a policy of rooming-in and treating NAS in the postnatal wards until day 10, 47.5% of infants were admitted to the neonatal unit (NNU). 40% of these admissions were for ongoing treatment of NAS. For term infants admitted to NNU, the median duration of total hospital stay was 17 days; non-admitted term infants remained in hospital for a median of 7 days. Infants of drug misusing mothers represented 2.9% of hospital births, but utilised 18.2% of NNU cot days. 44.7% of infants received pharmacological treatment for NAS. The likelihood of an infant requiring treatment for NAS was independently related to prescribed maternal methadone dose rather than associated polydrug misuse (p<0.01). Breast feeding was associated with reduced risk of requiring treatment for NAS (OR 0.52: 95% CI 0.33 to 0.84). 21% of infants were born preterm; gestational age did not influence the likelihood of the infant receiving treatment for NAS.

Conclusions Infants born to drug misusing mothers draw heavily on health care resources. The most important predictor of NAS is the prescribed maternal methadone dose. Breast feeding may protect against the development of NAS and should be actively promoted in the management of pregnant drug misusing women.