The aim was to determine the risk factors associated with severe acidosis during labor in newborns at term.

This was a retrospective monocentric case-control study, from January 2018 to December 2020. Cases included were all births with pH <7.0 at birth, single pregnancy, >37 weeks, without severe fetal malformation, and with an attempted vaginal delivery. For each included case, two controls were selected. These were the two deliveries immediately preceding the case, with pH >7.0 and no exclusion criteria. The two groups were compared as pairs, followed by a multivariate analysis of factors associated with the occurrence of severe acidosis.

Eighty-seven cases of severe acidosis were compared with 174 controls. After multivariate analysis, factors associated with the occurrence of acidosis were induction (odds ratio (OR) 2.41, confidence interval (CI) 95 %, 1.10–5.26), meconium fluid during labor (OR 4.38, CI 95 %, 1.14–16.78), the presence of uterine hyperstimulation (OR 3.15, CI 95 %, 1.45–6.83), and the occurrence of a sentinel event (shoulder dystocia, cord prolaps, uterine rupture) with OR 11.74, CI 95 %, 2.93–46.97. Conversely, increasing gestational age at delivery in weeks was found to be a protective factor (OR 0.33, CI 95 %, 0.24–0.46).

Several factors have been identified as being associated with the occurrence of acidosis. Their presence should alert the on-call team. The main factor, however, was the occurrence of a sentinel event, which is difficult to predict.