Chronic and gestational hypertension in pregnancy

At a glance

• Hypertensive disorders complicate about 5 to 10% of pregnancies. Chronic hypertension predates pregnancy or 20 weeks; gestational hypertension appears after 20 weeks without organ involvement.
• Both carry a high risk of superimposed pre-eclampsia, so every assessment looks for it. See pre-eclampsia and eclampsia.
• SOMANZ 2023 (the current Australian guideline) treats to 135/85 or less with labetalol, nifedipine or methyldopa.
• Swap ACE inhibitors and ARBs before conception or as soon as pregnancy is confirmed. Give aspirin 150 mg at night before 16 weeks to women with chronic hypertension.
• Hypertension in pregnancy is a cardiovascular risk marker for life. Follow up postpartum and yearly.

Definitions

Hypertension is a systolic of 140 mmHg or more and/or a diastolic of 90 mmHg or more, confirmed on repeat measurement and again at least 4 hours later. Measure seated with the arm at heart level, using Korotkoff V for diastolic and a large cuff when arm circumference is over 33 cm.

Category	Definition (SOMANZ 2023)
Chronic hypertension	Before pregnancy or before 20 completed weeks; essential or secondary
Gestational hypertension	New after 20 weeks, no maternal or fetal features of pre-eclampsia, resolves within 3 months
Pre-eclampsia	New hypertension after 20 weeks plus new organ or uteroplacental involvement
Superimposed pre-eclampsia	Pre-eclampsia features on chronic hypertension or renal disease
White coat hypertension	High clinic BP, normal ambulatory or home BP
Masked hypertension	Normal clinic BP, high ambulatory or home BP (new category in SOMANZ 2023)
Severe hypertension	160 systolic and/or 110 diastolic or more: treat urgently

• BP falls in the first half of pregnancy, with a nadir around 16 to 20 weeks. A woman first seen at 14 weeks with "normal" BP can still have chronic hypertension that reappears in the third trimester.
• Hypertension that persists beyond 12 weeks postpartum is reclassified as chronic.
• White coat hypertension isn't benign: SOMANZ cites progression to persistent hypertension after 20 weeks, and 8% develop pre-eclampsia. Use ABPM to sort it out.

Chronic hypertension

Causes and work-up

• Most is essential, often with obesity, older maternal age or a family history.
• Look for a secondary cause in young women, severe or resistant hypertension, or hypokalaemia: renal parenchymal disease, renal artery stenosis (fibromuscular dysplasia), primary aldosteronism, phaeochromocytoma, Cushing syndrome, coarctation, sleep apnoea.
• Baseline at booking: creatinine, electrolytes, urine PCR (so later proteinuria can be interpreted), LFTs, FBC, glucose, and an ECG if long-standing. This gives a reference for later pre-eclampsia bloods.
• Aldosterone to renin ratio is unreliable in pregnancy because renin and aldosterone both rise. Screen before conception or after birth.
• Pitfall: phaeochromocytoma can mimic pre-eclampsia and is lethal at delivery or under anaesthesia. Check plasma metanephrines if BP is labile or paroxysmal. See hypertension in kidney disease for renal causes.

Preconception

• Plan pregnancy with BP controlled and medicines changed.
• ACE inhibitors and ARBs: stop before conception or as soon as pregnancy is confirmed. Second and third trimester exposure causes fetal renal failure, oligohydramnios, limb contractures and skull hypoplasia. First trimester exposure carries at most a small risk and is not an indication to end the pregnancy.
• Spironolactone (antiandrogenic effects on a male fetus) and atenolol (fetal growth restriction) are avoided. Thiazides are usually stopped because they reduce plasma volume.
• Start folic acid. Women with chronic kidney disease, diabetes or obesity may need the higher dose.

Management in pregnancy

Who to treat, and to what target

• SOMANZ 2023: treat chronic and gestational hypertension to 135/85 or less.
• CHIPS (2015) compared diastolic targets of 85 and 100 mmHg. Tight control didn't change perinatal loss or neonatal care, but reduced severe maternal hypertension (27.5% vs 40.6%).
• CHAP (2022) randomised 2,408 women with mild chronic hypertension to treatment below 140/90 or treatment only at 160/105. The composite of pre-eclampsia with severe features, preterm birth before 35 weeks, abruption and perinatal death fell from 37.0% to 30.2%. Small-for-gestational-age births did not increase. ACOG changed its treatment threshold to 140/90 in response.
• Pitfall: stopping antihypertensives in the second trimester because BP is "normal" was common practice. Under SOMANZ 2023, keep treating to target and reduce only for low readings or symptoms.

Oral drugs

Drug	Dose range	Watch for
Labetalol	100 to 400 mg, three to four times daily	Avoid in asthma; can mask hypoglycaemia
Nifedipine modified release	20 to 60 mg twice daily	Headache, flushing, ankle oedema; avoid in aortic stenosis
Methyldopa	250 to 750 mg, three to four times daily	Sedation, depression, raised LFTs, positive Coombs test; avoid with a history of depression
Hydralazine (oral)	12.5 to 50 mg, three to four times daily	Reflex tachycardia and headache; best as an add-on
Clonidine	75 to 300 micrograms, three to four times daily	Rebound hypertension if stopped suddenly

• SOMANZ found no outcome difference between labetalol, nifedipine and methyldopa. Choose on comorbidity, access and preference. Add a second agent from another class before maximising the first.
• Oxprenolol, once a first-line Australian choice, is no longer available.

Preventing pre-eclampsia

• Aspirin 150 mg at night, started before 16 weeks (ideally from 12 weeks), stopped between 34 weeks and birth. Chronic hypertension is a high-risk factor on its own. ASPRE (2017) showed 150 mg reduced preterm pre-eclampsia by 62% in screen-positive women.
• Calcium 1 g/day or more if dietary intake is below 1 g/day (SOMANZ 1C).
• Moderate exercise of 2.5 to 5 hours a week. SOMANZ does not recommend salt restriction, vitamins C, D or E, omega-3, statins or metformin for prevention.

Surveillance

	Chronic hypertension	Gestational hypertension
Review	At least 4-weekly if controlled	At least weekly
Urine protein	Every visit (compare with baseline)	Every visit
Bloods (FBC, EUC, LFT)	If BP control worsens or symptoms appear	Same
Fetal growth scan	At least monthly	At least monthly

• Home BP monitoring with a validated device is supported, but it doesn't replace scheduled antenatal visits.
• Admit for severe hypertension (160/110 or more), headache, visual change, epigastric or chest pain, breathlessness, vomiting or fetal concern.

Gestational hypertension

• Diagnose only after excluding pre-eclampsia: urine PCR under 30 mg/mmol, normal platelets, creatinine and transaminases, and normal fetal growth.
• Up to 25% of women initially labelled with gestational hypertension progress to pre-eclampsia. Onset before 32 to 34 weeks carries the highest risk.
• A normal sFlt-1/PlGF ratio (38 or less) helps rule out pre-eclampsia over the next 1 to 4 weeks where available.

Timing of birth

• SOMANZ 2023 found inadequate evidence to mandate planned birth at 36 to 37+6 weeks for chronic or gestational hypertension, and recommends an individual plan.
• HYPITAT (2009) enrolled women at 36 to 41 weeks with gestational hypertension or mild pre-eclampsia. Induction reduced poor maternal outcomes compared with expectant management.
• ACOG (Committee Opinion 831) suggests birth at 38 to 39+6 weeks for chronic hypertension without medication, 37 to 39+6 weeks if medicated and controlled, and 37 weeks for gestational hypertension.
• Superimposed pre-eclampsia or severe hypertension changes the plan.

Postpartum

• BP often peaks on days 3 to 6. Women can develop pre-eclampsia or eclampsia for the first time after birth.
• Switch methyldopa to another agent because of its link with postnatal depression. NICE NG133 says to stop it within 2 days of birth, and this is common practice. SOMANZ 2023 lists methyldopa among acceptable postpartum agents and leaves the choice to shared decision-making.
• Breastfeeding-compatible options: nifedipine, labetalol, enalapril, captopril, metoprolol. Enalapril suits women with proteinuria or diabetes.
• SOMANZ conditionally advises against routine NSAIDs for analgesia in women with pre-eclampsia; short inpatient use is acceptable if nothing else works.
• Follow-up (SOMANZ): review within 1 week of discharge; at 3 to 6 months check BP (consider ABPM), urine ACR or PCR, BMI, fasting glucose and lipids; then yearly for 5 to 10 years. Screen for postnatal depression with the EPDS.
• Pre-eclampsia roughly doubles later cardiovascular disease and nearly quadruples later chronic hypertension (meta-analysis of over 10 million women cited by SOMANZ); gestational and chronic hypertension also raise long-term risk. Record it as a cardiovascular risk factor.

Special groups

• Aboriginal and Torres Strait Islander women have higher rates of chronic hypertension, diabetes and kidney disease in pregnancy. Check urine ACR and renal function at booking, start aspirin early, and plan care locally where possible.
• Rural and remote women with early-onset or severe hypertension may need transfer to a centre with neonatal intensive care before 34 weeks.
• Pre-existing diabetes or CKD adds risk: see pre-existing diabetes in pregnancy.

Pitfalls

• Mid-pregnancy BP fall hides chronic hypertension. Booking after 20 weeks makes chronic and gestational hypertension hard to tell apart.
• Proteinuria at booking means renal disease until proven otherwise; superimposed pre-eclampsia then needs other features, or a ratio test, to diagnose.
• Don't use atenolol or continue ACE inhibitors and ARBs in pregnancy.
• An abrupt rise in antihypertensive needs is pre-eclampsia until bloods and fetal assessment say otherwise.
• Gestational hypertension that hasn't resolved by 12 weeks postpartum is chronic hypertension and needs work-up.