What are the normal and abnormal blood pressure ranges in pregnancy?

Blood Pressure Ranges in Pregnancy: Normal and Abnormal Values

In pregnancy, blood pressure should be maintained below 140/90 mmHg, with severe hypertension defined as ≥160/110 mmHg requiring immediate treatment to reduce maternal morbidity and mortality. 1

Normal Blood Pressure Values in Pregnancy

Normal blood pressure in pregnancy is characterized by:

• Normotension: <140/90 mmHg 1
• Normal 24-hour ABPM values before 22 weeks: 1
  • 24-hour average: <126/76 mmHg
  • Awake average: <132/79 mmHg
  • Sleep average: <114/66 mmHg

It's important to note that blood pressure typically decreases in early pregnancy and rises gradually toward term. Blood pressure values that were previously considered "normal" (120-139/80-89 mmHg) are now recognized as potentially concerning.

Abnormal Blood Pressure Categories

Chronic Hypertension

• Definition: BP ≥140/90 mmHg diagnosed before pregnancy or before 20 weeks' gestation 1
• White-coat hypertension: Office BP ≥140/90 mmHg but normal home BP <135/85 mmHg (not entirely benign; increased risk for preeclampsia) 1

Gestational Hypertension

• Definition: New-onset hypertension (≥140/90 mmHg) at or after 20 weeks' gestation without proteinuria 1
• Diagnosis requires: Sustained elevation on 2 measurements at least 4 hours apart 1

Preeclampsia

• Definition: Gestational hypertension plus proteinuria (≥0.3g/day) OR evidence of other organ dysfunction 1
• Can occur postpartum 1

Severity Classification

• Mild to moderate hypertension: 140-159/90-109 mmHg 1
• Severe hypertension: ≥160/110 mmHg (medical emergency requiring hospitalization) 1

Risk Implications of Different BP Ranges

Recent evidence shows that even prehypertension (120-139/80-89 mmHg) before 20 weeks is associated with:

• 2.85 times higher risk of developing hypertensive disorders of pregnancy 2
• 59% increased risk of small-for-gestational-age births 3

In women with both diabetes and chronic hypertension, achieving BP <130/80 mmHg is associated with better outcomes than 130-139/80-89 mmHg, including:

• Lower risk of preeclampsia with severe features
• Reduced risk of indicated preterm birth before 35 weeks
• Lower NICU admission rates 4

Treatment Thresholds and Targets

When to Initiate Treatment

• For women with gestational hypertension, pre-existing hypertension with superimposed gestational hypertension, or hypertension with organ damage: Start treatment at BP ≥140/90 mmHg 1, 5
• For other pregnant women: Consider treatment at BP ≥150/95 mmHg 1

Target Blood Pressure

• General target: <140/90 mmHg 1, 5
• Lower limit: Do not reduce diastolic BP below 80 mmHg 5
• For women with diabetes and hypertension: Consider tighter control with target <130/80 mmHg 4

Severe Hypertension Management

• Emergency threshold: ≥160/110 mmHg requires immediate hospitalization 1
• Target during acute treatment: Decrease mean BP by 15-25% and aim for 140-150/90-100 mmHg 5

Medication Considerations

First-line Medications

• Methyldopa
• Labetalol
• Long-acting nifedipine (not short-acting) 5

Contraindicated Medications

• ACE inhibitors
• Angiotensin receptor blockers (ARBs)
• Direct renin inhibitors
• Mineralocorticoid receptor antagonists
• Neprilysin inhibitors 1, 5

Postpartum Considerations

• BP often rises after delivery, peaking 3-6 days postpartum 1, 5
• Monitor BP for 72 hours in hospital and for 7-10 days postpartum for women with hypertensive disorders 1, 5
• Women with history of preeclampsia have nearly 4 times higher risk of developing chronic hypertension later in life 1, 5

Clinical Pearls

• White-coat hypertension affects up to 25% of patients; confirm elevated office readings with home BP monitoring or 24-hour ABPM 1
• Home BP monitoring devices should be validated against calibrated equipment before use in pregnancy 1
• The CHAP trial demonstrated that treating mild chronic hypertension to target <140/90 mmHg improved pregnancy outcomes without increasing small-for-gestational-age births 6
• Low-dose aspirin (81 mg/day) is recommended by the end of the first trimester for women with type 1 or type 2 diabetes to reduce preeclampsia risk 1

By understanding these blood pressure ranges and their implications, clinicians can better identify, monitor, and manage hypertensive disorders in pregnancy to improve maternal and fetal outcomes.