Gestation-Specific Vital Sign Reference Ranges in Pregnancy

Aug 12 2020 , India

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OBJECTIVE: To estimate normal ranges for maternal vital
signs throughout pregnancy, which have not been well
defined in a large contemporary population.
METHODS: We conducted a three-center, prospective,
longitudinal cohort study in the United Kingdom from
August 2012 to September 2017. We recruited women at
less than 20 weeks of gestation without significant
comorbidities with accurately dated singleton pregnancies.
We measured participants’ blood pressure (BP),
heart rate, respiratory rate, oxygen saturation and temperature
following standardized operating procedures at
4–6 weekly intervals throughout pregnancy.

RESULTS: We screened 4,279 pregnant women, 1,041
met eligibility criteria and chose to take part. Systolic and
diastolic BP decreased slightly from 12 weeks of gestation:
median or 50th centile (3rd–97th centile) 114
(95–138); 70 (56–87) mm Hg to reach minimums of 113
(95–136); 69 (55–86) mm Hg at 18.6 and 19.2 weeks of
gestation, respectively, a change (95% CI) of 21.0 (22 to
0); 21 (22 to 21) mm Hg. Systolic and diastolic BP then
rose to a maximum median (3rd–97th centile) of 121
(102–144); 78 (62–95) mm Hg at 40 weeks of gestation,
a difference (95% CI) of 7 (6–9) and9 (8–10) mm Hg,
respectively. The median (3rd–97th centile) heart rate

was lowest at 12 weeks of gestation: 82 (63–105) beats
per minute (bpm), rising progressively to a maximum of
91 (68–115) bpm at 34.1 weeks. SpO2 decreased from 12
weeks of gestation: median (3rd–97th centile) 98% (94–
99%) to 97% (93–99%) at 40 weeks. The median (3rd–
97th centile) respiratory rate at 12 weeks of gestation
was 15 (9–22), which did not change with gestation.
The median (3rd–97th centile) temperature at 12 weeks
of gestation was 36.7 (35.6–37.5)°C, decreasing to
a minimum of 36.5 (35.3–37.3)°C at 33.4 weeks.

CONCLUSION: We present widely relevant, gestationspecific
reference ranges for detecting abnormal BP,
heart rate, respiratory rate, oxygen saturation and temperature
during pregnancy. Our findings refute the
existence of a clinically significant BP drop from 12
weeks of gestation.

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