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.