Abstract: We found one new included study in this updated version. In total, our updated review includes 11 trials (with 753 participants). The low quality of evidence showed no significant differences in average Apgar scores at one minute (N = six trials, 519 participants; 95% confidence (CI) -0.16 to 0.31, P = 0.53) and at five minutes (N = six trials, 519 participants; 95% CI -0.06 to 0.06, P = 0.98). None of the 11 trials reported maternal desaturation. The very low quality of evidence showed that in comparison to room air, women in labour receiving supplementary oxygen had higher maternal oxygen saturation (N = three trials, 209 participants), maternal PaO2 (oxygen pressure in the blood; N = six trials, 241 participants), UaPO2 (foetal umbilical arterial blood; N = eight trials, 504 participants; 95% CI 1.8 to 4.9, P < 0.0001) and UvPO2 (foetal umbilical venous blood; N = 10 trials, 683 participants). There was high heterogeneity among these outcomes. A subgroup analysis showed no significant difference in UaPO2 between the two intervention groups in low-risk studies, whereas the high-risk studies showed a benefit for the neonatal oxygen group. Overall, we found no convincing evidence that giving supplementary oxygen to healthy term pregnant women during elective caesarean section under regional anaesthesia is either beneficial or harmful for either the mother or the foetus' short-term clinical outcome as assessed by Apgar scores. Although, there were significant higher maternal and neonatal blood gas values and markers of free radicals when extra oxygen was given, the results should be interpreted with caution due to the low grade quality of the evidence.

Plain-language summary: This updated Cochrane review included 11 studies involving 753 participants. The studies compared maternal (mother) and neonatal (foetal) outcomes when pregnant women received extra oxygen versus room air. Oxygen was given to the women in different ways (at any flow rate or concentration via any oxygen delivery device). Overall, the results of this updated review reach the same conclusions as the original published review. None of the 11 included trials reported maternal desaturation. No differences were noted in routine measures of foetal wellbeing (Apgar scores) when mothers who received extra oxygen were compared with those who did not. The pregnant women receiving extra oxygen in comparison with room air had significantly higher oxygen saturation (three trials) and partial pressure of oxygen in arterial blood (five trials), as well as a significantly higher partial pressure of oxygen in both the umbilical artery and the umbilical vein (eight and 11 trials, respectively). Two trials reported higher markers of free radicals (perhaps indicating stress from excess oxygen) in mothers and foetuses when extra oxygen was given, but this is of no clinical significance Overall, we found no convincing evidence that giving oxygen in this situation is either beneficial or harmful for either the mother or the foetus. None of the 11 studies focused on maternal changes in oxygen saturation (defined as maternal saturation less than 90%). We graded the quality of evidence as low for the primary outcome (Apgar scores), and very low for the secondary outcomes (maternal oxygen saturation; partial pressure of oxygen in arterial blood, the umbilical artery and the umbilical vein). The reasons for our grading were risk of bias and inconsistency of the results.