What are normal blood pressure ranges during pregnancy and how are blood pressure changes managed?

Blood Pressure Changes During Pregnancy

Normal Blood Pressure Ranges in Pregnancy

Blood pressure normally decreases in early pregnancy, reaching its lowest point in the second trimester (approximately 15 mmHg lower than pre-pregnancy values), then gradually rises back to or slightly above baseline by the third trimester. 1

Specific Normal Values by Gestational Age

• Systolic blood pressure: Lowest at 10 weeks gestation at 110.4 mmHg, rising to 116.0 mmHg at 40 weeks (mean increase of 5.6 mmHg) 2
• Diastolic blood pressure: Lowest at 21 weeks gestation at 65.9 mmHg, rising to 72.8 mmHg at 40 weeks (mean increase of 6.9 mmHg) 2
• Heart rate: Increases from 79.3 beats/min at 10 weeks to 86.9 beats/min at 40 weeks (mean increase of 7.6 beats/min) 2

24-Hour Ambulatory Blood Pressure Monitoring Reference Values

For women before 22 weeks gestation, normal values should be below: 1

• 24-hour average: <126/76 mmHg
• Awake average: <132/79 mmHg
• Sleep average: <114/66 mmHg

These values are slightly lower than thresholds used for non-pregnant women. 1

Classification of Hypertension in Pregnancy

Chronic Hypertension

• Definition: Hypertension present before pregnancy or diagnosed before 20 weeks gestation 1
• Diagnostic threshold: BP ≥140/90 mmHg in clinic or ≥135/85 mmHg at home 1
• Confirmation: Should ideally be confirmed by 24-hour ambulatory BP monitoring or home BP monitoring to exclude white-coat hypertension (which affects up to 25% of patients with elevated clinic readings) 1

Gestational Hypertension

• Definition: New-onset hypertension developing after 20 weeks gestation without proteinuria 1, 3
• Diagnostic threshold: BP ≥140/90 mmHg 1
• Risk: Approximately 25% will progress to preeclampsia 3, 4

White-Coat Hypertension

• Definition: Elevated office/clinic BP (≥140/90 mmHg) but normal BP at home (<135/85 mmHg) 1
• Clinical significance: Not entirely benign—conveys increased risk for preeclampsia 1

Transient Gestational Hypertension

• Definition: De novo hypertension that develops during pregnancy but resolves without treatment 1
• Risk: Associated with approximately 40% risk of developing true gestational hypertension or preeclampsia later in pregnancy 1

Management of Blood Pressure Changes

When to Initiate Treatment

For chronic hypertension or gestational hypertension with risk factors:

• Initiate treatment at BP ≥140/90 mmHg (office) or ≥135/85 mmHg (home) 3, 4
• Target BP: Diastolic 85 mmHg and systolic 110-140 mmHg 3

For uncomplicated chronic hypertension without organ damage:

• Treatment threshold may be ≥150/95 mmHg per some European guidelines 4

Severe Hypertension Requiring Urgent Treatment

BP ≥160/110 mmHg represents a hypertensive emergency requiring immediate treatment within 15 minutes in a monitored setting to prevent maternal stroke. 3, 4, 5

Acute management options: 3, 5

• Oral immediate-release nifedipine
• Intravenous labetalol
• Intravenous hydralazine

First-Line Antihypertensive Medications

Methyldopa, labetalol, and long-acting nifedipine are the preferred agents for ongoing BP control in pregnancy. 3, 5

Baseline Laboratory Assessment for Chronic Hypertension

All women with chronic hypertension should have the following tests at first diagnosis to establish baseline values (important for detecting superimposed preeclampsia, which complicates up to 25% of these pregnancies): 1

1. Complete blood count (hemoglobin and platelet count)
2. Liver enzymes (AST, ALT, LDH) and function tests (INR, bilirubin, albumin)
3. Serum creatinine, electrolytes, and uric acid
4. Urinalysis and microscopy, plus protein-to-creatinine ratio or albumin-to-creatinine ratio
5. Renal ultrasound if serum creatinine or urine testing are abnormal

Important Clinical Considerations

Blood Pressure Measurement Technique

• Diastolic BP should be measured at Korotkoff phase V (disappearance of sound) rather than phase IV (muffling), as phase V has better reproducibility 1
• Awake ambulatory BP measurements are 11-12 mmHg higher (systolic) and 5-11 mmHg higher (diastolic) than relaxed clinic measurements 6
• Manual BP measurement reports higher diastolic values than automated measurement (mean difference 4.9 mmHg), so the two methods cannot be used interchangeably 2

Home Blood Pressure Monitoring

• Approximately 25% of automated home BP devices differ from standard sphygmomanometry 1
• All women should have their home BP device checked against a calibrated device validated for use in pregnancy before relying on home measurements 1
• In the absence of severe hypertension, rely on average BP over several days rather than single readings 1

Monitoring Strategy

For women with elevated BP in early pregnancy:

• Document normal BP either pre-pregnancy or in early pregnancy (before 12 weeks) to distinguish chronic from gestational hypertension 1
• BP measured after 12 weeks that appears normal may reflect the physiologic first-trimester BP fall, potentially masking underlying chronic hypertension 1

For transient gestational hypertension:

• Requires more frequent monitoring than usual for remainder of pregnancy 1
• Assess proteinuria at 3 months postpartum 1

Indications for Hospitalization

Admit to hospital for: 3

• BP ≥160/110 mmHg (severe hypertension)
• Development of preeclampsia features
• Neurological signs or symptoms
• Inability to control BP with ≥3 antihypertensive drug classes

Timing of Delivery

• Gestational hypertension without preeclampsia: Delivery can be delayed until 39+6 weeks if BP remains controlled, fetal monitoring is reassuring, and preeclampsia has not developed 3
• Preeclampsia: Delivery at term (≥37 weeks) is recommended 3, 5

Long-Term Cardiovascular Risk

Women with gestational hypertension or preeclampsia have increased lifetime cardiovascular risk and require annual medical review lifelong. 3, 5

Recent meta-analysis data show that even BP in the 120-139/80-89 mmHg range before 20 weeks gestation is associated with 2.85-fold increased risk of developing hypertensive disorders of pregnancy compared to BP <120/80 mmHg. 7