Hypertensive disorders in pregnancy: aspirin, BP targets, and postnatal care

Pre-eclampsia, the blood pressure threshold that changes everything

Hypertensive disorders of pregnancy are the most common serious medical complication of pregnancy in Australia, affecting an estimated 5–10% of all pregnancies. Pre-eclampsia — the most clinically significant form — contributes to approximately 10% of maternal deaths in Australia per AIHW maternal deaths data, and is associated with preterm birth, fetal growth restriction, neonatal intensive care admission, and both short- and long-term morbidity for mother and baby.

The disorders sit on a spectrum: chronic hypertension (pre-existing), gestational hypertension (new after 20 weeks, no organ involvement), pre-eclampsia (gestational hypertension with proteinuria or organ involvement), eclampsia (seizure), and HELLP (haemolysis, elevated liver enzymes, low platelets). Knowing which category a patient is in — and when it is changing — is the fundamental clinical task.

SOMANZ 2014 (under revision) and RANZCOG 2022 remain the primary Australian guideline documents.

A. Core clinical — the AU general-practice framework

Classification

The ISSHP 2018 international classification — adopted by SOMANZ and RANZCOG — distinguishes:

Category	Definition
Chronic hypertension	Pre-pregnancy diagnosis OR blood pressure ≥140/90 before 20 weeks; persists >12 weeks postpartum
Gestational hypertension	New blood pressure ≥140/90 after 20 weeks; no proteinuria; no end-organ disease; resolves by 12 weeks postpartum
Pre-eclampsia	Gestational hypertension PLUS proteinuria (uPCR ≥30 mg/mmol) OR any maternal end-organ involvement OR uteroplacental dysfunction
Superimposed pre-eclampsia	Chronic hypertension with new proteinuria or new end-organ disease
Eclampsia	Pre-eclampsia with new-onset generalised tonic-clonic seizure
HELLP syndrome	Pre-eclampsia with haemolysis, ALT/AST ≥2× upper limit of normal, and platelets below 100 × 10⁹/L

Severity bands: mild (140–149/90–99 mmHg), moderate (150–159/100–109 mmHg), severe (≥160/110 mmHg — treat as an emergency without delay).

Risk stratification and aspirin prophylaxis

At the booking visit, every pregnant woman should be stratified for pre-eclampsia risk. Per RANZCOG 2022 and NICE NG133 2019, aspirin 100–150 mg nightly is offered to women with one high-risk factor or two or more moderate-risk factors:

High-risk factors:

• Previous pre-eclampsia (especially early-onset or severe)
• Chronic hypertension
• Chronic kidney disease
• Antiphospholipid syndrome or systemic lupus erythematosus
• Pre-existing diabetes (type 1 or type 2)
• Inherited thrombophilia

Moderate-risk factors:

• First pregnancy (primiparity)
• Age over 40
• BMI ≥30
• Family history of pre-eclampsia in mother or sister
• Multiple pregnancy
• IVF or donor egg conception
• Inter-pregnancy interval greater than 10 years
• Aboriginal and Torres Strait Islander background

Aspirin must be started by 12–16 weeks to modify the trophoblast invasion and spiral artery remodelling process that underlies pre-eclampsia. The ASPRE trial (Rolnik, NEJM 2017) showed that 150 mg aspirin nightly from 11–14 weeks reduced the rate of preterm pre-eclampsia by 62% in high-risk women identified by first-trimester screening. Starting after 20 weeks provides minimal protection.

Monitoring through pregnancy

Blood pressure and urinalysis should be checked at every antenatal visit. Any reading of ≥140/90 mmHg in a woman who was previously normotensive after 20 weeks requires:

• Confirmation after four hours (unless ≥160/110 — treat immediately)
• Urine protein-creatinine ratio (uPCR)
• Full blood count, urea and electrolytes, liver function tests, and serum urate

Rising urate supports a pre-eclampsia diagnosis. Falling platelets or rising transaminases indicate progression toward HELLP.

Home blood pressure monitoring is a useful adjunct in high-risk women but does not replace clinic measurement.

Blood pressure management

The CHIPS trial (Magee, NEJM 2015) compared tight control (target below 140/90 mmHg) with less-tight control (target below 160/110 mmHg) in 987 women with non-severe chronic or gestational hypertension in pregnancy. Tight control reduced severe hypertension without increasing fetal harm. The CHAP trial (Tita, NEJM 2022) confirmed this in chronic hypertension. Both SOMANZ and RANZCOG 2022 now support a target blood pressure below 140/90 mmHg throughout pregnancy.

First-line oral antihypertensives per eTG and AMH:

Agent	Dose	Notes
Labetalol	100–200 mg twice to three times daily (max 1200 mg/day)	Avoid in asthma; extensive safety data
Methyldopa	250–500 mg twice to three times daily (max 3 g/day)	Long safety record; switch away postpartum (depression risk)
Nifedipine MR (Adalat Oros)	30–60 mg daily (max 120 mg/day)	Convenient once-daily dosing; flushing/headache common initially

Strictly avoid throughout pregnancy: ACE inhibitors (ramipril, perindopril, enalapril), angiotensin receptor blockers (irbesartan, candesartan, telmisartan) — fetotoxic, causing oligohydramnios, fetal renal dysplasia, and neonatal hypotension. Also avoid atenolol (associated with fetal growth restriction) and spironolactone (anti-androgenic to male fetus).

Severe acute hypertension (≥160/110 mmHg) is a medical emergency requiring immediate in-hospital treatment:

• IV labetalol 20 mg bolus, doubling every 10 minutes to a maximum of 80 mg, then infusion
• IV hydralazine 5–10 mg bolus every 20 minutes
• Oral nifedipine IR 10 mg (by mouth only — sublingual route causes uncontrolled precipitous drops)
• Target a controlled, moderate reduction — avoid lowering by more than 25% in one hour to protect uteroplacental perfusion

Pre-eclampsia management

Women with pre-eclampsia, HELLP, or eclampsia require inpatient obstetric management. The GP role in this phase is recognition, stabilisation, and urgent transfer.

Magnesium sulfate is the guideline-supported treatment for eclampsia prevention in severe pre-eclampsia and for treating eclamptic seizures. The MAGPIE trial (Altman, Lancet 2002) demonstrated a 58% relative risk reduction in eclampsia in women with pre-eclampsia treated with magnesium sulfate compared with placebo. Monitoring of reflexes, respiratory rate, and urine output is required; calcium gluconate is the antidote.

Corticosteroids for fetal lung maturity are given as betamethasone 11.4 mg intramuscularly twice, 24 hours apart, for all women with pre-eclampsia at less than 34+6 weeks per Australian Pregnancy Care Guidelines.

Delivery timing

The only definitive treatment for pre-eclampsia is delivery of the placenta. Current guidelines support:

• Pre-eclampsia at term (≥37 weeks) — immediate delivery, as supported by HYPITAT-I (Koopmans, Lancet 2009), which showed reduced maternal complications without neonatal harm
• Severe pre-eclampsia at 34–37 weeks — deliver; expectant management only with very close monitoring in a tertiary facility
• Late preterm (34–36 weeks) with mild stable pre-eclampsia — expectant management reduces neonatal respiratory complications without significant added maternal risk; individualised specialist decision
• HELLP or eclampsia — stabilise then deliver immediately, regardless of gestation

Postpartum care

Blood pressure does not resolve at delivery — it commonly worsens and peaks on day three to six after birth. Monitoring protocol:

• Blood pressure days three to five postpartum
• Repeat at one week, two weeks, and the six-week postnatal review
• Continue antihypertensive medication as needed; wean once stable blood pressure is achieved
• Switch methyldopa within 48 hours postpartum — postpartum depression risk
• ACE inhibitors are now appropriate after delivery and are compatible with breastfeeding at recommended doses (enalapril, captopril are preferred choices per AMH and MotherSafe)
• Repeat full blood count, renal function, and liver function tests at the six-week review; refer if persistently abnormal

B. Evidence base — the key trials

ASPRE (Rolnik, NEJM 2017): This multicentre RCT randomised 1776 high-risk women (identified by combined first-trimester screening including uterine artery Doppler, maternal blood pressure, serum analytes, and risk factors) to aspirin 150 mg or placebo from 11–14 weeks. Preterm pre-eclampsia was reduced by 62% (RR 0.38, 95% CI 0.20–0.74). Term pre-eclampsia was not significantly reduced. This underpinned the shift to 150 mg (rather than 100 mg) in many Australian protocols, though 100 mg remains acceptable per RANZCOG 2022.

CHIPS (Magee, NEJM 2015): This international trial of 987 women showed tight blood pressure control (target diastolic 85 mmHg) reduced severe hypertension by more than 50% compared with less-tight control (target 100 mmHg), without increasing adverse fetal outcomes. CHIPS resolved the long-standing concern that treating moderate hypertension in pregnancy harmed fetal growth.

CHAP (Tita, NEJM 2022): This US RCT of 2408 women with mild chronic hypertension confirmed that treatment to a target below 140/90 mmHg reduced the composite of severe hypertension, preterm birth, placental abruption, and fetal or neonatal death (RR 0.82, 95% CI 0.74–0.92) without increasing small-for-gestational-age infants. CHAP strengthened the case for early and consistent blood pressure treatment in pregnancy.

MAGPIE (Altman, Lancet 2002): This landmark RCT in 10,110 women with pre-eclampsia across 33 countries established magnesium sulfate as superior to placebo in preventing eclampsia (RR 0.42). Magnesium sulfate is now the universal standard for eclampsia prevention in severe pre-eclampsia.

HYPITAT-I (Koopmans, Lancet 2009): This Dutch RCT of 756 women with mild pre-eclampsia or gestational hypertension at 36–41 weeks showed that immediate delivery reduced maternal adverse outcomes substantially compared with expectant management, with no meaningful difference in neonatal outcomes. Delivery at term for pre-eclampsia is now standard.

Calcium for prevention (Hofmeyr, Cochrane 2018): This Cochrane systematic review found that calcium supplementation (1–2 g/day) in women with low dietary calcium intake reduces the risk of pre-eclampsia by around 55% and is WHO-recommended in calcium-deficient populations. Most Australian diets provide adequate calcium; assess dietary intake and supplement only where insufficient.

C. Prevention and lifestyle considerations

Beyond aspirin and calcium, the following modifiable factors reduce pre-eclampsia risk:

• Pre-conception weight management — BMI ≥30 is a moderate risk factor; weight optimisation before pregnancy reduces risk and improves obstetric outcomes overall
• Smoking cessation — important for vascular and placental health; nicotine replacement therapy is preferred in pregnancy over continuation of smoking; avoid varenicline and bupropion
• Medication review before conception — women on ACE inhibitors or ARBs should switch to a pregnancy-safe antihypertensive before conception; best done at preconception planning appointments
• Mediterranean dietary pattern — endothelial protection; reducing inflammatory load across the pregnancy
• Modest sodium reduction (to below 5 g salt per day) — avoid aggressive restriction, which may compromise fluid balance
• Regular moderate exercise — at least 150 minutes per week; reduces blood pressure, manages weight, and improves mood
• Home blood pressure monitoring — validated upper-arm device; useful for detecting masked hypertension and improving treatment adherence in women with chronic hypertension

Women with a previous history of pre-eclampsia benefit from pre-conception specialist review, medication rationalisation, and aspirin planning before the next pregnancy.

D. Australian operations

MBS items

• Items 16590 / 16591 — GP shared antenatal care attendances
• Item 16622 — high-risk antenatal attendance (complex pre-eclampsia cases)
• Items 23 / 36 / 44 — standard GP consultations (postpartum monitoring, long-term follow-up)
• Item 715 — ATSI Health Assessment
• Item 73529 — urine protein-creatinine ratio (key diagnostic test in monitoring)
• Items 65070 / 66500 — full blood count, liver function tests, urea and electrolytes, urate (key surveillance bloods)
• Item 55700 range — obstetric ultrasound for fetal growth and Doppler assessment
• Item 2700 / 2701 — mental health care plan (for postpartum anxiety, depression, birth trauma following pre-eclampsia)

PBS prescribing

• Labetalol, methyldopa, nifedipine MR (Adalat Oros) — General Schedule; no authority required
• Hydralazine (acute severe hypertension) — General Schedule (IV supply typically from hospital)
• Magnesium sulfate — hospital supply for acute management
• Aspirin 100 mg tablets — over-the-counter; 150 mg requires one tablet plus half a tablet where that dose is used
• Low-molecular-weight heparin (enoxaparin) — General Schedule for VTE prophylaxis in pre-eclampsia with additional risk factors

Key Australian services and resources

• SOMANZ — Society of Obstetric Medicine Australia and New Zealand; guideline source and clinical training
• MotherSafe (1800 647 848) — free NSW-based medication-in-pregnancy telephone advisory service; available nationally
• AAPEC — Australian Action on Pre-eclampsia; patient advocacy, support network, information
• Pregnancy, Birth and Baby (1800 882 436) — nurse-midwife helpline and consumer resources
• HealthDirect — consumer information

Long-term cardiovascular surveillance

Pre-eclampsia predicts approximately double the lifetime risk of cardiovascular disease — coronary artery disease, stroke, and chronic hypertension — compared with women who had normotensive pregnancies. The GP is the general practice clinician who sees these women annually after obstetric care ends. Annual cardiovascular risk assessment from six months postpartum is recommended: blood pressure, weight, fasting lipids, fasting glucose, smoking status, and family history review.

E. Special populations

Aboriginal and Torres Strait Islander women: higher rates of severe pre-eclampsia and adverse perinatal outcomes. ATSI Health Assessment (item 715) and antenatal shared care should be used to ensure risk stratification and aspirin initiation at booking. Cultural safety and involvement of Aboriginal Health Workers improve engagement and outcomes.

Women with chronic hypertension: review and switch teratogenic antihypertensives (ACE inhibitors, ARBs, spironolactone) to labetalol, methyldopa, or nifedipine MR ideally before conception. Aspirin is a high-risk indication and should start at 12 weeks. These women need at least fortnightly antenatal review from 28 weeks, and closer surveillance for the superimposition of pre-eclampsia on their existing hypertension.

Women with chronic kidney disease: very high risk of pre-eclampsia and fetal growth restriction; shared care with nephrology is standard. Blood pressure targets may be tighter than in the general pregnant population.

Multiple pregnancies: pre-eclampsia risk is approximately three times higher in twin than singleton pregnancies. Most are managed with specialist obstetric involvement throughout.

Women with antiphospholipid syndrome: high-risk; aspirin plus low-molecular-weight heparin (therapeutic or prophylactic dose) is the standard combination; specialist haematology or rheumatology input is standard.

When to escalate

Emergency (000 and obstetric notification simultaneously):

• Eclamptic seizure
• Suspected stroke or sudden neurological change
• Severe chest pain or breathlessness suggesting pulmonary oedema
• Antepartum haemorrhage
• Suspected placental abruption

Same-day obstetric assessment unit:

• Blood pressure ≥160/110 mmHg, confirmed or unconfirmed
• New hypertension after 20 weeks with any symptoms — severe headache, visual disturbance (scotomata, photopsia, blurred vision), epigastric or right upper quadrant pain, nausea or vomiting
• Hyperreflexia or clonus on examination
• Reduced fetal movements
• Suspected HELLP (falling platelets, rising transaminases, epigastric pain)
• New hypertension or worsening BP in the first week postpartum

Within 24–48 hours obstetric or maternal medicine clinic:

• New gestational hypertension without features, stable blood pressure
• Rising uPCR in a previously monitored patient
• Uncontrolled chronic hypertension in pregnancy despite medication

What this article is and is not

This is general health information drawn from SOMANZ 2014, RANZCOG 2022, the Australian Pregnancy Care Guidelines, eTG, AMH, and the landmark ASPRE, CHIPS, CHAP, MAGPIE, and HYPITAT trials. It is not personal medical advice and does not create a doctor–patient relationship. Management of hypertensive disorders in pregnancy is complex and time-sensitive — decisions about aspirin, antihypertensives, delivery timing, and postnatal monitoring are made by the treating obstetric and GP team who know the individual clinical picture.

For consumer information: HealthDirect — Pre-eclampsia, Pregnancy, Birth and Baby 1800 882 436, AAPEC, MotherSafe 1800 647 848.

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Sources cited

1. SOMANZ — Hypertension in Pregnancy 2014
2. RANZCOG — Hypertensive disorders of pregnancy 2022
3. Australian Pregnancy Care Guidelines (Department of Health)
4. eTG complete — Obstetrics and gynaecology
5. AMH — Antihypertensives in pregnancy
6. Rolnik et al. — ASPRE trial (NEJM 2017)
7. Magee et al. — CHIPS trial (NEJM 2015)
8. Tita et al. — CHAP trial (NEJM 2022)
9. Altman et al. — MAGPIE trial (Lancet 2002)
10. Koopmans et al. — HYPITAT-I (Lancet 2009)
11. Hofmeyr et al. — Calcium supplementation (Cochrane 2018)
12. ISSHP 2018 — Classification and management of pre-eclampsia
13. NICE NG133 — Hypertension in pregnancy 2019
14. AIHW — Maternal deaths in Australia
15. HealthDirect — Pre-eclampsia
16. Pregnancy, Birth and Baby — Pre-eclampsia
17. AAPEC — Australian Action on Pre-eclampsia
18. MotherSafe