Gestational Hypertension Diagnostic Criteria
Gestational hypertension is diagnosed when a pregnant woman at ≥20 weeks gestation develops new-onset blood pressure ≥140/90 mmHg on at least two separate occasions, without evidence of proteinuria or other features of preeclampsia. 1, 2
Critical Timing: The 20-Week Threshold
The 20-week gestational age serves as the fundamental dividing line for classifying hypertensive disorders in pregnancy 3, 1:
- Before 20 weeks: Any hypertension is classified as chronic (pre-existing) hypertension 3, 2
- At or after 20 weeks: New-onset hypertension is classified as either gestational hypertension or preeclampsia 1, 2
This cutoff is based on the expected physiologic decline in blood pressure during the first 20 weeks of normal pregnancy 3.
Blood Pressure Thresholds
The diagnostic threshold is systolic BP ≥140 mmHg AND/OR diastolic BP ≥90 mmHg 1, 2, 4:
Confirmation Requirements
The diagnosis requires proper confirmation with repeated measurements 1, 2:
- For severe hypertension (≥160/110 mmHg): Confirmation should occur within 15 minutes with repeated measurements 1, 2, 4
- For non-severe hypertension: Confirmation requires at least two elevated readings on two separate occasions, either over several hours during the same visit or on two consecutive antenatal visits 1, 2
Essential Exclusion: Rule Out Preeclampsia
To diagnose gestational hypertension, you must exclude features of preeclampsia 1:
- No proteinuria: <0.3 g/day in 24-hour collection or <30 mg/mmol urinary creatinine in spot sample 2
- No maternal organ dysfunction: Check complete blood count, liver enzymes, and serum creatinine in asymptomatic women with new-onset hypertension 1
- No severe features: Absence of visual disturbances, severe persistent headache, upper abdominal pain, or other warning signs 4
Important Clinical Caveats
White Coat Hypertension
Up to 25% of patients with elevated clinic readings may have white coat hypertension (≥140/90 mmHg in clinic but <135/85 mmHg at home) 1, 2. Consider ambulatory BP monitoring or home monitoring before confirming the diagnosis 1.
Normal ambulatory BP values in pregnancy 1:
- 24-hour average: <126/76 mmHg
- Awake average: <132/79 mmHg
- Asleep average: <114/66 mmHg
Risk of Progression
Approximately 20-25% of gestational hypertension cases will progress to preeclampsia 1, 4, necessitating:
- More frequent monitoring throughout the remainder of pregnancy 1
- Regular screening for proteinuria 4
- Home blood pressure measurements 1
- Evaluation of proteinuria at 3 months postpartum 1
Blood Pressure Trajectory Patterns
Women who develop gestational hypertension often demonstrate a blunted decline or increase in systolic BP before 20 weeks, rather than the normal physiologic decrease 3. This atypical pattern may help identify at-risk individuals earlier in pregnancy 3.