Definition of Pregnancy-Induced Hypertension
Pregnancy-induced hypertension is defined as new-onset hypertension with systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg occurring at or after 20 weeks of gestation in a previously normotensive woman 1, 2.
Diagnostic Criteria
The blood pressure thresholds must be confirmed with repeated measurements:
- For severe hypertension (systolic BP ≥160 and/or diastolic BP ≥110 mmHg): Confirm within 15 minutes 1
- For non-severe hypertension (systolic BP 140-159 and/or diastolic BP 90-109 mmHg): Repeat readings over several hours 1
Critical Timing Distinction
The 20-week gestational age cutoff is the key diagnostic marker that differentiates pregnancy-induced hypertension from chronic hypertension 2:
- Before 20 weeks: Classified as chronic hypertension
- At or after 20 weeks: Classified as gestational hypertension or preeclampsia (if proteinuria or target organ involvement present)
Important Caveat About Early Pregnancy Blood Pressure
Normal blood pressure documented either prepregnancy or in early pregnancy (before 12 weeks) is essential for accurate diagnosis 1. This is because:
- Blood pressure naturally decreases during the first trimester
- A "normal" BP first measured after 12 weeks may actually reflect this physiological drop, masking underlying chronic hypertension
- Women who develop pregnancy-induced hypertension often show a blunted decline or actual increase in systolic BP before 20 weeks, rather than the expected physiological decrease 2
Categories of Pregnancy-Induced Hypertension
The term encompasses two main conditions:
- Gestational hypertension: Hypertension alone without proteinuria or other organ involvement
- Preeclampsia: Hypertension with proteinuria (≥0.3 g protein in 24-hour urine or 1+ on dipstick) or other evidence of target organ involvement 3
Measurement Technique
Use a liquid crystal sphygmomanometer when available, or a validated automated device specifically tested in pregnancy and preeclampsia 1. Aneroid devices require regular calibration as 50% may have readings >10 mmHg off compared to mercury devices 1. Ensure proper cuff size (large cuff if mid-upper arm circumference >33 cm) 1.
Special Diagnostic Scenarios
When prior BP is unknown: If a woman presents with hypertension at or after 20 weeks and earlier BP records are unavailable, manage as gestational hypertension or preeclampsia during pregnancy, then investigate postpartum 1. The diagnosis becomes clear if BP fails to normalize within 3 months postpartum, indicating underlying chronic hypertension 1.