Objective: To compare the carbon footprint of caesarean and vaginal birth. Design: Life cycle assessment. Setting: Tertiary maternity units and home births in the UK and the Netherlands Methods: A life cycle assessment, including: equipment use, energy, analgesia, hospital stay, waste, sterilisation and laundry, was conducted using primary data combined with data from published sources. Main Outcome Measures: ‘Carbon footprint’ (in kgCO 2e) Results: Excluding analgesia, the carbon footprint of a caesarean birth in the UK was 31.21 kgCO 2e, compared with 12.47 kgCO 2e for vaginal birth in hospital and 7.63 kgCO 2e at home. In the Netherlands the carbon footprint of a caesarean was higher (32.96 kgCO 2e), but lower for vaginal birth in hospital and home (10.74 and 6.27 kgCO 2e respectively). Emissions associated with analgesia for vaginal birth were: 0.08 kgCO 2e (opioid analgesia), 0.75 kgCO 2e (remifentanil), 1.2 kgCO 2e (epidural) and 237.33 kgCO 2e (nitrous oxide with oxygen). Differences in analgesia use resulted in a lower average carbon footprint for vaginal birth in the Netherlands than the UK (11.64 vs. 193.26 kgCO 2e). Conclusion: The carbon footprint of a caesarean is higher than for vaginal birth if analgesia is excluded, but this is very sensitive to the analgesia used; use of nitrous oxide with oxygen multiplies the carbon footprint of vaginal birth 25-fold. Alternative methods of pain relief or nitrous oxide destruction systems would lead to a substantial improvement in carbon footprint. Although clinical need and maternal choice are paramount, protocols should consider the environmental impact of different choices.