Masked Hypertension in Pregnancy

Masked hypertension in pregnancy is normal clinic blood pressure (below 140/90 mmHg) with raised readings at home or on 24 hour monitoring (135/85 mmHg or more). It is missed by routine antenatal measurement. It matters because it carries risks of preeclampsia, growth restriction, preterm birth and later cardiovascular disease comparable to those of sustained hypertension.

• Risk factors: chronic kidney disease, diabetes, obesity, night shift work, stress, previous preeclampsia.
• Found in women with normal clinic readings, especially in high risk groups.
• Home or ambulatory monitoring is needed to find it.

Women are often well, with normal clinic readings, though some have headache, swelling or a poor growth fundal height. Home readings are high.

• Clinic readings 120 to 139/80 to 89 mmHg.
• Sometimes new proteinuria.
• Differential diagnosis: chronic hypertension, preeclampsia, gestational hypertension, white coat hypertension, measurement error, anxiety at home, stimulant use.
• Complications: preeclampsia, eclampsia, fetal growth restriction, preterm birth, abruption, stillbirth, postpartum hypertension.

The diagnosis is made by out of clinic measurement.

• Home blood pressure for 7 days with a validated upper arm device, two readings morning and evening; an average of 135/85 mmHg or more confirms masked hypertension.
• 24 hour ambulatory monitoring: daytime average 135/85 mmHg or more or night time average 120/70 mmHg or more.
• Urine protein to creatinine ratio, full blood count, creatinine, liver enzymes, uric acid, glucose.
• Ultrasound for growth and umbilical artery Doppler; uterine artery Doppler at 20 to 24 weeks.

The principle is home guided blood pressure control, with surveillance for preeclampsia and growth restriction.

• Supportive: teach home blood pressure measurement; rest; reduce stress; stop smoking and alcohol; low salt cooking without strict restriction; blood pressure review each visit with home diary.
• Pharmacological: labetalol 200 mg oral every 8 to 12 hours (maximum 2.4 g daily) or nifedipine modified release 30 to 60 mg oral once daily (maximum 120 mg) or methyldopa 250 to 500 mg oral 8-hourly (maximum 3 g daily), aiming for 110 to 135/85 mmHg at home; aspirin 150 mg oral at night from 12 weeks to 36 weeks; calcium 1.5 g elemental oral daily where intake is low; stop ACE inhibitors, angiotensin receptor blockers and diuretics; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour for 24 hours if severe features develop.
• Procedures: delivery at 37 to 39 weeks if blood pressure is controlled, and earlier for preeclampsia or growth restriction.
• Special groups: asthma uses nifedipine instead of labetalol; kidney disease and diabetes need tighter targets and closer surveillance.
• Red flags: home blood pressure 160/110 mmHg or more, headache, visual change, epigastric pain, new proteinuria, reduced fetal movements.
• Follow-up: review every 2 weeks with home diary and urine protein; growth scans every 4 weeks from 28 weeks; postnatal blood pressure at 6 hours, daily for 5 days, then at 2 and 6 weeks; annual blood pressure.