• Base excess;
  • electronic fetal monitoring;
  • fetal acidemia;
  • fetal heart rate;
  • inter-observer reproducibility;
  • intra-observer reproducibility

Objective  To evaluate whether a standardised algorithm to interpret fetal heart rate (FHR) tracings during the entire length of labour can predict umbilical artery base excess at birth, and to investigate its inter- and intra-observer reproducibility.

Design  Retrospective study.

Setting  Obstetrics and gynaecology department at a tertiary referral centre in a university hospital.

Population  Group 1: 152 consecutive, generally low-risk, labouring women. Group 2: mixed group of 30 women who delivered a fetus with pH < 7.00 and 30 women who delivered a fetus with pH ≥ 7.00.

Methods  Intrapartum FHR tracings were retrospectively and blindly evaluated by two independent assessors using an algorithm proposed by Ross and Gala to predict fetal base excess at birth.

Main outcome measures  The accuracy in predicting the base excess values of newborns was expressed as the proportion of FHR tracings in which the operator was able to correctly calculate the actual base excess at birth (approximation of ±2 mmol/l). Inter- and intra-observer reproducibility were estimated using the Pearson correlation coefficient.

Results  In the group of 152 low-risk labouring women, the two assessors correctly predicted the umbilical artery base excess in 73.1 and 76.3% of cases, respectively. Inter-observer (Pearson correlation coefficient = 0.75) and intra-observer (Pearson correlation coefficient = 0.80 and 0.82 for the first and second assessor, respectively) reproducibility was very good. In the 30 fetuses that were acidemic, the first and second observers correctly predicted base excess values in 23 (76.7%) and 21 (70%) cases, respectively (inter-observer reproducibility, Pearson correlation coefficient = 0.72).

Conclusions  The algorithm proposed by Ross and Gala may be a valuable tool to estimate changes in umbilical base excess during active labour, with a high inter- and intra-observer reproducibility.