BACKGROUND AND PURPOSE:

• Data defining normal ranges for maternal vital signs in pregnancy are limited
  • Data required to develop better early warning tools
• Green et al. (Obstetrics & Gynecology, 2020) determined physiologic vital sign measurements using standardized techniques throughout pregnancy

METHODS:

• Three-center, prospective, longitudinal cohort study
• Setting
  • The United Kingdom (2012 to 2017)
• Participants
  • <20 weeks | Accurately dated | Singleton pregnancies | No significant comorbidities or complications
• Study design
  • Measurements every 4 to 6 weeks  
  • Vitals
    • BP
    • Heart rate
    • Respiratory rate
    • Oxygen saturation
    • Temperature

RESULTS:

• 1,041 women
• Systolic and diastolic BP decreased slightly from 12 weeks of gestation to 18.6 to 19.2 weeks
  • Median (3rd to 97th centile) at 12 weeks
    • Systolic: 114 (95 to 138) mm Hg
    • Diastolic: 70 (56 to 87) mm Hg
  • Minimum BP
    • Systolic at 18.6 weeks: 113 (95 to 136) mm Hg
    • Diastolic at 19.2 weeks: 69 (55 to 86) mm Hg
  • A change (95% CI) of
    • Systolic: −1.0 (−2 to 0) mm Hg
    • Diastolic: −1 (−2 to −1) mm Hg
• Systolic and diastolic BP then both rose to a maximum median at 40 weeks’ gestation
  • Maximum median (3rd to 97th centile)
    • Systolic: 121 (102 to 144) mm Hg
    • Diastolic: 78 (62 to 95) mm Hg
  • A change (95% CI) of
    • Systolic: 7 (6 to 9) mm Hg
    • Diastolic: 9 (8 to 10) mm Hg
• Median heart rate
  • Lowest at 12 weeks’ gestation with a maximum at 34.1 weeks
  • Median (3rd to 97th centile) at 12 weeks’
    • 82 (63 to 105) bpm
  • Maximum median (3rd to 97th centile) at 34.1 weeks
    • 91 (68 to 115) bpm
• SpO2
  • Decreased from 12 weeks’ gestation to 40 weeks’ gestation
  • Median (3rd to 97th centile) at 12 weeks
    • 98% (94 to 99%)
  • Median at 40 weeks
    • 97% (93 to 99%)
• Respiratory rate
  • Median respiratory rate at 12 weeks of gestation did not change with gestation
  • Median (3rd to 97th centile) at 12 weeks
    • 15 (9 to 22)
• Temperature
  • Median temperature at 12 weeks decreased to a minimum at 33.4 weeks
  • Median (3rd to 97th centile) at 12 weeks
    • 36.7 (35.6 to 37.5) °C
  • Median at 33.4 weeks
    • 36.5 (35.3 to 37.3) °C

CONCLUSION:

• Gestational age specific centile ranges can be used to identify women who are at risk for pregnancy complications
• The authors note that their data can set appropriate thresholds
  • SpO2 of 94% is still within the normal range
  • Heart of 115 was to upper limit of normal and waiting till HR of 120 may be too high a threshold for a maternal warning alert
  • The classic 10 to 15 mm Hg BP drop was not seen in this study and therefore using <90 mm Hg  systolic as a trigger for sepsis may too low

Learn More – Primary Sources:

Gestation-Specific Vital Sign Reference Ranges in Pregnancy

Related ObG Topics:

Pregnancy-Related Deaths in the U.S.: How Many are Preventable?

Is Maternal Core Temperature Elevated Beyond a Critical Threshold During Exercise in Pregnancy?

New ACC Blood Pressure Guidelines in Pregnancy: Should We Start Monitoring Prior to 140/90?

SMFM & CMQCC Guidelines: Making the Diagnosis of Sepsis in Pregnancy