Determination of Normal Ranges of Shock Index and Other Haemodynamic Variables in the Immediate Postpartum Period: A Cohort Study

PLoS One. 2016 Dec 20;11(12):e0168535. doi: 10.1371/journal.pone.0168535. eCollection 2016.


Objective: To determine the normal ranges of vital signs, including blood pressure (BP), mean arterial pressure (MAP), heart rate (HR) and shock index (SI) (HR/systolic BP), in the immediate postpartum period to inform the development of robust obstetric early warning scores.

Study design: We conducted a secondary analysis of a prospective observational cohort study evaluating vital signs collected within one hour following delivery in women with estimated blood loss (EBL) <500ml (316 women) delivering at a UK tertiary centre over a one-year period. Simple and multiple linear regression were used to explore associations of demographic and obstetric factors with SI.

Results: Median (90% reference range) was 120 (100-145) for systolic BP, 75 (58-90) for diastolic BP, 90 (73-108) for MAP, 81 (61-102) for HR, and 0.66 (0.52-0.89) for SI. Third stage Syntometrine® administration was associated with a 0.03 decrease in SI (p = 0.035) and epidural use with a 0.05 increase (p = 0.003). No other demographic or obstetric factors were associated with a change in shock index in this cohort.

Conclusion: This is the first study to determine normal ranges of maternal BP, MAP, HR and SI within one hour of birth, a time of considerable haemodynamic adjustment, with minimal effect of demographic and obstetric factors demonstrated. The lower 90% reference point for systolic BP and upper 90% reference point for HR correspond to triggers used to recognise shock in obstetric practice, as do the upper 90% reference points for systolic and diastolic BP for obstetric hypertensive triggers. The SI upper limit of 0.89 in well postpartum women supports current literature suggesting a threshold of 0.9 as indicating increased risk of adverse outcomes.

Publication types

  • Multicenter Study
  • Observational Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Blood Pressure / physiology*
  • Female
  • Heart Rate / physiology*
  • Humans
  • Postpartum Period / physiology*
  • Prospective Studies
  • United Kingdom