Clinical intrapartum factors associated with low umbilical artery pH: A study of 14 092 term singleton spontaneous vaginal births

: Aims To evaluate the variation in umbilical cord arterial pH values among term newborns delivered by spontaneous vaginal birth with normal Apgar scores, and to investigate the associations between pH levels, and especially low pH values (≤7.10), and maternal, intrapartum, and early neonatal characteristics. Methods This retrospective birth register study included data on umbilical artery (UA) pH values and clinical perinatal information from 14 092 term (>36 gestational weeks) singleton pregnancies resulting in spontaneous vaginal delivery, with neonates having a 5-minute Apgar score >7 at Kuopio University Hospital, Finland, between 2008 and 2018. Maternal, intrapartum, and early neonatal characteristics were prospectively recorded at the time of delivery. Associations between clinical variables and low UA pH values (≤7.10) were further evaluated using multivariable logistic regression analysis. Results The mean UA pH value after spontaneous vaginal birth was 7.26; the 50 th , 10 th and 3 rd percentile values were 7.27, 7.16 and 7.10, respectively. Low pH values were independently associated with a longer duration of the active second stage of labor (adjusted odds ratios [aORs] 2.23─6.41) and the duration of ruptured membranes (aORs 1.62─1.96), lower parity (aORs 1.49─1.96), maternal height ≤160 cm (aOR 1.94), excessive gestational weight gain (≥18 kgs) (aOR 1.39), labor augmentation with oxytocin (aOR 1.46) and maternal infection (aOR 2.09). Neither amniotomy nor labor induction was associated with low umbilical artery pH levels in multivariable analysis. Conclusion We demonstrated that several clinical and maternal characteristics were associated with low umbilical artery pH values. Recognition of these factors may improve our understanding of the mechanisms underlying adverse intrapartum outcomes and facilitate the early identification of fetuses at increased risk of low umbilical artery pH at birth.