Objective: To evaluate predictive factors for respiratory depression at birth in infants >/=37 weeks.
Design: A population-based cohort study of respiratory depression at birth at term and post-term.
Setting: Nova Scotia, Canada.
Population: All 126 604 nonanomalous, singleton deliveries >/=37 weeks in cephalic presentation from 1988-2002.
Methods: An analysis of maternal, antenatal, intrapartum, and neonatal factors associated with respiratory depression at birth >/=37 weeks.
Main outcome measures: A composite outcome of delay in initiating and maintaining respiration after birth, 5-minute Apgar score </= 3, or neonatal seizures due to hypoxic-ischaemic encephalopathy.
Results: The rate of respiratory depression at birth with delay in respiration was 5.2/1000, with Apgar </= 3 1.0/1000 live births, and with neonatal seizures 0.7/1000. A composite of any of the three respiratory depressions at birth criteria showed comparable low rates with spontaneous delivery (4.4/1000) and elective caesarean (4.8/1000). Compared with elective caesarean delivery, vacuum (13.2/1000, relative risk [RR] 3.97, P < 0.001), forceps (8.8/1000, RR 1.84, P= 0.003), failed vacuum (13.3/1000, RR 2.76, P= 0.005), failed forceps (33.3/1000, RR 6.93, P < 0.001), and caesarean in labour (17.0/1000, RR 3.54, P < 0.001) had significantly higher rates of the composite outcome.
Conclusion: Overall, the rate of respiratory depression at birth in the term infant was low and the serious manifestation of seizures was less than 1 in 1000. There was a significant relationship between operative delivery in labour and respiratory depression at birth.