What is diagnostic of chronic hypertension in pregnancy?

Diagnostic Criteria for Chronic Hypertension in Pregnancy

Chronic hypertension in pregnancy is diagnosed when hypertension (≥140/90 mmHg) is either documented before pregnancy or develops before 20 weeks of gestation. 1

Diagnostic Thresholds

Blood pressure must be ≥140 mmHg systolic OR ≥90 mmHg diastolic, confirmed on at least two separate occasions. 1, 2 This distinguishes chronic hypertension from gestational hypertension, which by definition occurs at or after 20 weeks. 1

Key Timing Distinction

• Before 20 weeks gestation = Chronic hypertension 1, 2
• At or after 20 weeks gestation = Gestational hypertension 1, 2

Confirmation Methods

Office/Clinic Measurements

• Elevated office BP (≥140/90 mmHg) should be confirmed by 24-hour ambulatory blood pressure monitoring (ABPM) or home BP monitoring, or at minimum by repeated measurements over hours at the same visit or on 2 consecutive antenatal visits. 1
• Up to 25% of patients with elevated clinic BP have white-coat hypertension, which can be largely avoided by having BP recorded by a nurse rather than a physician, using repeated readings. 1

Ambulatory and Home Monitoring

Before 22 weeks, ABPM values diagnostic of hypertension are: 1

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

For home BP monitoring, values ≥135/85 mmHg are diagnostic (compared to office threshold of ≥140/90 mmHg). 1

Practical Diagnostic Approach

When Pre-Pregnancy BP is Known

• A documented diagnosis of hypertension before pregnancy automatically qualifies as chronic hypertension in pregnancy. 1, 2

When Pre-Pregnancy BP is Unknown

• Many women will not have had BP measured within months before becoming pregnant, so first trimester BP is relied upon to define normal or high BP. 1
• If hypertension is first detected before 20 weeks without prior documentation, it is classified as chronic hypertension. 1
• If hypertension is detected at or after 20 weeks with unknown earlier BP, the woman should be managed as if she has gestational hypertension or preeclampsia until proven otherwise. 3

Important Caveats

White-Coat Hypertension

• Elevated office/clinic BP (≥140/90 mmHg) but normal BP at home or work (<135/85 mmHg) is not entirely benign and conveys increased risk for preeclampsia. 1
• All women should have either home BP monitoring or 24-hour ABPM before accepting a diagnosis of true essential hypertension. 1

Home BP Device Validation

• Approximately 25% of automated home BP devices differ from standard sphygmomanometry, so all devices should be checked against a calibrated sphygmomanometer or automated device validated for use in pregnancy before relying on home measurements. 1

Etiology

• Most cases (majority) are due to essential hypertension, usually accompanied by family history and often by overweight or obesity. 1
• Secondary causes are uncommon; when present in childbearing age, the cause is usually underlying primary renal parenchymal disorder (reflux nephropathy or glomerulonephritis) and less commonly fibromuscular hyperplasia or primary hyperaldosteronism. 1

Baseline Testing at Diagnosis

Once chronic hypertension is diagnosed, the following baseline tests should be performed to facilitate later detection of superimposed preeclampsia (which complicates up to 25% of these pregnancies): 1, 3

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