The effects of maternal labour analgesia on the fetus.

Maternal labour pain and stress are associated with progressive fetal metabolic acidosis. Systemic opioid analgesia does little to mitigate this stress, but opioids readily cross the placenta and cause fetal-neonatal depression and impair breast feeding. Pethidine remains the most widely used, but alternatives, with the possible exception of remifentanil, have little more to offer. Inhalational analgesia using Entonox is more effective and, being rapidly exhaled by the newborn, is less likely to produce lasting depression. Neuraxial analgesia has maternal physiological and biochemical effects, some of which are potentially detrimental and some favourable to the fetus. Actual neonatal outcome, however, suggests that benefits outweigh detrimental influences. Meta-analysis demonstrates that Apgar score is better after epidural than systemic opioid analgesia, while neonatal acid-base balance is improved by epidural compared to systemic analgesia and even compared to no analgesia. Successful breast feeding is dependent on many factors, therefore randomized trials are required to elucidate the effect of labour analgesia.