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Objective To assess the effect of epidural versus systemic labour analgesia on funic acid–base status at birth.

Design A systematic review of trials, both randomised and non-randomised, comparing epidural with systemic opioid analgesia.

Population Babies of 2102 mothers taking part in trials comparing epidural with systemic analgesia in five countries.

Methods From the published and unpublished figures obtained from authors, fetal pH data from 12 studies (eight randomised) (1098 babies in the epidural group + 1004 controls) and base excess from 8 studies (four randomised) (856 epidural + 842 controls) were subjected to random effect meta-analysis.

Main outcome measures Umbilical artery pH and base excess values.

Results Fetal pH was higher in the epidural than in the control group in the randomised trials (difference +0.009, 95% CI +0.002 to +0.015), but when all studies were included, the difference was not significant (+0.004, 95% CI −0.005 to +0.014). Fetal base excess was higher in the epidural group in the four randomised studies (difference +0.779 mEq/L, 95% CI +0.056 to +1.502) and in all eight studies (difference +0.837 mEq/L, 95% CI +0.330 to +1.343).

Conclusion Umbilical artery pH is influenced by maternal hyperventilation. Base excess is therefore a better index of metabolic acidosis after labour. Epidural analgesia is associated with improved neonatal acid–base status, suggesting that placental exchange is well preserved in association with maternal sympathetic blockade and good analgesia. Although epidural analgesia may cause maternal hypotension and fever, longer second stage of labour and more instrumental vaginal deliveries, these potentially adverse factors appear to be outweighed by benefits to neonatal acid–base status.