Normal and Concerning Blood Pressure Changes in Pregnancy
Normal Physiologic Blood Pressure Changes
During normal pregnancy, systolic and diastolic blood pressure typically increase by approximately 8 mmHg from early pregnancy to term, with median values rising from 113/69 mmHg in the second trimester to 121/78 mmHg at 40 weeks gestation. 1
Expected BP Trajectory Throughout Pregnancy
First and Second Trimesters: Blood pressure initially declines in early pregnancy, with diastolic BP typically falling about 10 mmHg below baseline by the second trimester due to systemic vasodilation 1
Third Trimester: BP gradually increases and may normalize to pre-pregnancy values by term, with progressive increases averaging ≈8 mmHg for both systolic and diastolic measurements 1
Normal ranges at 12 weeks: For nulliparous women, mean SBP is 112 mmHg (range 89-136) and DBP is 65 mmHg (range 49-82) 2
Normal ranges at 37 weeks: Mean SBP increases to 116 mmHg (range 92-140) and DBP to 70 mmHg (range 52-88) 2
Concerning Blood Pressure Elevations
Diagnostic Thresholds for Hypertension
Hypertension in pregnancy is defined as systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg on two separate occasions, regardless of the increase from baseline. 1, 3, 4
Critical Warning Signs Requiring Immediate Action
Severe hypertension (≥160/110 mmHg) constitutes a medical emergency requiring immediate hospitalization 1, 5
Any BP ≥170 mmHg systolic or ≥110 mmHg diastolic demands urgent treatment within a monitored setting 1
Risk Stratification by BP Range
BP 120-139/80-89 mmHg before 20 weeks: This "elevated" range carries 2.85 times higher risk of developing hypertensive disorders compared to BP <120/80 mmHg, though not yet diagnostic of hypertension 6
BP 140-149/90-99 mmHg (mild hypertension): Requires non-pharmacological management initially, with close monitoring for progression 1, 3
BP 150-159/100-109 mmHg (moderate hypertension): Warrants initiation of antihypertensive therapy 3
BP ≥160/110 mmHg (severe hypertension): Requires urgent pharmacological intervention with IV labetalol, oral methyldopa, or oral nifedipine as first-line agents 1, 7, 5
Treatment Thresholds Based on Clinical Context
When to Initiate Antihypertensive Therapy
For women with gestational hypertension (with or without proteinuria) or pre-existing hypertension with superimposed gestational hypertension, treatment should begin at BP ≥140/90 mmHg. 1
For other pregnant women without these specific conditions, treatment is recommended when BP reaches ≥150/95 mmHg. 1, 3
Target Blood Pressure Goals
Therapeutic target: Maintain BP between 110-135/80-85 mmHg to reduce maternal complications while preserving uteroplacental perfusion 7, 5
Diastolic goal: Aim for DBP around 85 mmHg, with systolic BP kept below 160 mmHg 1
Avoid excessive lowering: Reduce or discontinue antihypertensives if diastolic BP falls below 80 mmHg to prevent compromised placental perfusion 1, 5
Postpartum Blood Pressure Patterns
Blood pressure peaks on days 3-5 postpartum for systolic and days 5-7 for diastolic measurements due to withdrawal of placental vasodilatory hormones and fluid mobilization. 1
BP should normalize by 2 weeks postpartum in women without hypertensive disorders of pregnancy 1
Methyldopa should be avoided postpartum due to risk of postnatal depression 1
Key Clinical Pitfalls to Avoid
Do not wait for a specific "increase from baseline" to diagnose hypertension—absolute values of ≥140/90 mmHg define hypertension regardless of prior readings 1, 3
Do not use hydralazine IV as first-line therapy for severe hypertension, as it causes more perinatal adverse effects than labetalol, methyldopa, or nifedipine 1, 7
Never use ACE inhibitors, ARBs, or direct renin inhibitors during pregnancy due to severe fetotoxicity including renal dysgenesis 7, 5, 3
Avoid excessive BP reduction below 90/60 mmHg, which can compromise uteroplacental perfusion 5