A summary of the 2023 Society of Obstetric Medicine of Australia and New Zealand (SOMANZ) hypertension in pregnancy guideline

Hypertensive disorders of pregnancy (HDP) affect 3–10% of all pregnancies globally.1,2,3 In Australia and New Zealand, 3–4% of pregnancies are affected by preeclampsia, a type of HDP that is associated with significant maternal and fetal morbidity and mortality.4,5,6,7 More recently, studies have demonstrated that HDP, particularly preeclampsia, are also associated with long term comorbid conditions in affected women and their offspring.8

The Society of Obstetric Medicine of Australia and New Zealand (SOMANZ) was established in 2005, through amalgamation of the Australasian Society for the Study of Hypertension in Pregnancy (ASSHP) and the Obstetric Medicine Group of Australasia (OMGA), and is committed to providing up‐to‐date guidance to improve maternal and obstetric outcomes in pregnant women with medical disorders. This guideline represents an update of the SOMANZ guidelines for the management of hypertensive disorders of pregnancy 2014.9 Knowledge has advanced significantly since publication of the last guideline and newer evidence has allowed for recommendations on screening for women who are at risk of developing preeclampsia, preventive interventions, and clinical use of angiogenic biomarkers.

Methods

The methodology for the guideline was developed in accordance with the National Health and Medical Research Council (NHMRC) standards for guidelines10 and was approved by NHMRC in December 2023, under section 14A of the National Health and Medical Research Council Act 1992. Detailed description of the methodology is accessible through the main guideline document and published methodology.11 Key stages included:

• establishing an expert multidisciplinary group of 28 members, comprised of a broad range of medical practitioners (obstetricians, primary care, intensive care, subspecialty physicians, and neonatologists), midwives, scientists, pharmacists, methodologists, First Nations People and consumer representatives;11
• identifying 39 clinical questions of priority, within the categories of screening, prevention and management;
• comprehensive literature searches for studies from 1970 to 2022, based on pre‐determined MeSH (Medical Subject Headings) keywords, through three main electronic databases (Medline, Cochrane Library, Embase);
• data extraction of selected literature, conducted independently by two members of the working group;
• meta‐analyses of extracted data through Review Manager 5.4 (RevMan; the Cochrane Collaboration, 2020; https://revman.cochrane.org/info);
• bivariate model analyses for sensitivity and specificity for diagnostic test accuracy through STATA18 (StataCorp);
• quality of evidence appraisal through the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach;12 and
• generation of recommendations based on the Evidence to Decision framework.13

Final recommendations were made with more than 60% of group members in agreement. The draft guideline was open for public consultation for six weeks, with 94 resulting comments addressed and incorporated into the guideline where appropriate.

Recommendations in the guideline are presented as either evidenced‐based recommendations or practice points.11 The main guideline document contains summary of meta‐analyses, rationale for recommendations and comparison of recommendations with key national and international guidelines. The guideline along with clinician and multilingual patient information sheets are accessible online at https://www.somanz.org/hypertension‐in‐pregnancy‐guideline‐2023/.11

The recommendations are based on literature published up to December 2022. Where indicated, the working group may update meta‐analyses and recommendations based on critical new data. Updates following publication of this guideline can be accessed through the SOMANZ website.11

Summary of recommendations

The recommendations are presented in eight parts and include definitions of HDP, screening for women at risk, and preventive and management strategies.

Part 1: definitions of hypertensive disorders of pregnancy

Recommendations on definitions of HDP are largely consistent with the previous version of this guideline and are based on expert consensus.9 New to the guideline is the definition of masked hypertension.

Hypertension in pregnancy is defined as systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg. These measurements should be confirmed by repeated readings (with three consecutive readings at least two minutes apart) within a minimum of four hours to confirm true hypertension. Accurate blood pressure measurement is important, as inaccuracies may result in variation of treatment.11

The recommended classifications of HDP are described in Box 1. Important updated points include the following:11

• proteinuria is a commonly recognised feature of preeclampsia but is not a mandatory criterion for the diagnosis of preeclampsia (refer to “Part 4.1: urine assessment for proteinuria” for more information); and
• at the time of publication, there remain limited data on inclusion of angiogenic markers as a diagnostic criterion for preeclampsia (refer to “Part 4.2: use of sFlt‐1/PlGF ratio” for more information).

The following investigations should be performed as part of the initial assessment of new onset hypertension (Practice point):

• full blood count — additional investigations for disseminated intravascular coagulation and/or haemolysis (coagulation studies, blood film, lactate dehydrogenase and fibrinogen) should be considered for significant thrombocytopenia or a rapid decline in haemoglobin concentration;
• electrolytes, urea and creatinine;
• liver function tests;
• proteinuria assessment — a dipstick assessment for proteinuria is clinically useful, readily available and easy to perform as an initial screening tool; however, where there is clinical suspicion for a HDP, a quantitative urine analysis (ie, urinary protein to creatinine ratio [uPCR]) should be performed (refer to “Part 4.1: urine assessment for proteinuria” for more information);
• angiogenic markers (eg, soluble fms‐like tyrosine kinase‐1 [sFlt‐1] to placental growth factor [PlGF] ratio) with a cut‐off < 38 can help rule out preeclampsia in women with clinical suspicion of preeclampsia after 20 weeks’ gestation and, if locally available, in a timely manner (refer to “Part 4.2: use of sFlt‐1/PlGF ratio” for more information);
• fetal assessment — ultrasound assessment for fetal growth, amniotic fluid volume (using amniotic fluid index or deepest vertical pocket), and umbilical artery Doppler; and
• cardiotocography assessment may be indicated according to hospital policy and gestation.

Following the diagnosis of a HDP, subsequent investigations and management of the diagnosed HDP should be undertaken as recommended in the main guideline document.11

Part 2: screening for women at risk of preeclampsia

Women should have their risk of preeclampsia assessed early in pregnancy to allow for consideration of preventive strategies (1B). There are clinical factors that may help in identifying women who are or who are not at increased risk of developing preeclampsia (Box 2). Risk assessment can be refined using combined first trimester screening (combined algorithm of maternal characteristics, biomarkers and sonographic assessment) (2B).

Where there are conflicting risk assessments based on clinical factors and combined first trimester screening, clinicians should discuss the risks and potential benefits of preventive strategies with women through a shared, informed decision‐making process.

At the time of publication, there were no published randomised controlled trials (RCTs) on the clinical use of combined first trimester screening, and the recommendations made were based on a diagnostic test accuracy assessment of 11 cohort studies. Furthermore, at the time of publication, combined first trimester screening is not widely accessible across Australia and New Zealand. The group acknowledges that there are ongoing studies on this topic and current recommendations are subject to review based on future updated data.

Part 3: prevention of preeclampsia

The recommendations on 14 pharmacological and two non‐pharmacological preventive interventions were made based on 118 RCTs (Box 3).

In summary, we recommend that 150 mg of oral aspirin (1B) at bedtime (2C) is commenced before 16 weeks’ gestation (1B) in women who have been identified at high risk of developing preeclampsia (Box 3). We recommend ceasing aspirin between 34 weeks’ gestation and birth (2B). The guideline includes an infographic that can be used to counsel women on the use of aspirin in pregnancy.11 We also recommend the use of supplemental calcium in women with a dietary calcium intake of less than 1 g per day (1C). The guideline includes a summarised dietary calcium intake calculator that can be used to ascertain women's dietary calcium intake.11 In addition to aspirin and supplemental calcium, moderate intensity exercise, in the form of aerobic, stretching and/or muscle resistance exercises, for a total of 2.5 to five hours a week, is recommended (Box 3) (2D). This guideline includes an infographic on exercising in pregnancy.11 At the time of publication, there remain inadequate data on the benefit of other pharmacological and non‐pharmacological interventions examined.11

Part 4: diagnosis of preeclampsia

This version of the guideline includes recommendations on the use of urinary albumin to creatinine ratio (uACR) for diagnosis of proteinuria in pregnancy as well as the clinical use of angiogenic markers.

In summary, we recommend that urine dipstick can be used as an initial screening tool; however, dipstick alone is inadequate to diagnose proteinuria in pregnancy (2B). For quantitative testing, a uPCR of ≥ 30 mg/mmol can be used (1B). Where uPCR is unavailable, a uACR with a cut‐off ≥ 8 mg/mmol can be used (2B).

Where available in a timely manner, the sFlt‐1:PlGF ratio with a cut‐off < 38 can be used in women over 20 weeks’ gestation with clinical suspicion of preeclampsia to rule out preeclampsia within one to four weeks of testing (2D). At the time of publication, the use of an elevated sFlt‐1:PlGF ratio (> 85) in diagnosing preeclampsia, determining fetal outcomes, severity of disease, timing of birth and routine screening in asymptomatic women are not recommended until more data are available (2D).

Similarly, more data on the clinical application of PlGF alone testing in women with clinical suspicion of preeclampsia are required before clinical implementation of testing based on PlGF alone in Australia and New Zealand. At the time of publication, both angiogenic biomarkers (sFlt‐1:PlGF ratio and PlGF alone) are not widely accessible in Australia and New Zealand. The group acknowledges that RCTs on this topic are ongoing and that the recommendations on the clinical application of angiogenic biomarkers are subject to a review based on updated data in the near future.

Part 5: management of chronic or gestational hypertension in pregnancy

Recommendations on five key clinical questions on the management of chronic or gestational hypertension were made based on 120 RCTs (Box 4).

We recommend that women with gestational or chronic hypertension should have blood pressure controlled to a target of ≤ 135/85 mmHg (1C). Where appropriate, home blood pressure monitoring (HBPM) with the use of a validated blood pressure device can be utilised in women with stable chronic or gestational hypertension (1B). The use of HBPM, however, should not replace the minimum recommended frequency of antenatal review according to the woman's parity and stage of pregnancy (Box 4). The guideline includes an infographic on HBPM and sample HBPM log.11

Oral agents such as labetalol, methyldopa and/or nifedipine can be used to manage stable hypertension (gestational hypertension, chronic hypertension, non‐severe hypertension in preeclampsia) (2C). The choice of agent should be individualised based on availability, women's clinical history and through a shared, informed decision‐making process (Box 4 and Box 5).

There remain inadequate data to suggest the need for planned birth before 37⁺⁶ weeks’ gestation in women with stable gestational or chronic hypertension and where there are no concerns for fetal wellbeing. The decision on the timing of birth should be individualised based on women's clinical history and through a shared, informed decision‐making process (Box 4) (2D).

Where indicated, ambulatory blood pressure monitoring should be considered to exclude white coat hypertension in women with isolated hypertension in pregnancy (in the absence of an established diagnosis of preeclampsia, chronic hypertension, or gestational hypertension; Box 4) (Practice point).

Part 6: management of preeclampsia

Recommendations in addressing nine key clinical questions on the management of preeclampsia were made based on 99 RCTs (Box 6).

Oral agents labetalol, methyldopa and/or nifedipine can be used in managing stable (non‐severe/non‐acute) hypertension in women with preeclampsia (Box 5 and Box 4) (2C). Short‐acting agents, such as intravenous hydralazine, intravenous labetalol, oral immediate release nifedipine or intravenous diazoxide are recommended in managing acute hypertension (≥ 160/110 mmHg; Box 6 and Box 7) (2C). The use of magnesium sulphate is strongly recommended in women who are at risk of eclampsia (Box 8 and Box 6) (1A).

Timing of birth for women with preeclampsia should be based on the maternal and fetal indications. Birth should be considered at any gestation in the event of significant deterioration. At ≥ 37 weeks’ gestation, birth should be initiated in women with preeclampsia (2D). At < 37 weeks’ gestation, the decision on expectant management or immediate birth should be made based on maternal and fetal stability and balanced against risks arising from preterm birth (Box 6) (2D).

For women at risk of preterm birth, the use of corticosteroid is recommended in women who are at risk of birth < 34 weeks’ gestation (2A). The use of magnesium sulphate for fetal neuroprotection is strongly recommended in women at risk of preterm birth at < 30 weeks’ gestation (Box 6) (2A).

As preeclampsia is a risk factor for venous thromboembolism (VTE), it is important to consider VTE prophylaxis in women with preeclampsia (Practice point). VTE risk assessment should be made based on local hospital or state‐based protocols or policies. In the absence of relevant guidance, this guideline includes a VTE risk assessment tool for use in women with preeclampsia.11

Part 7: immediate and short term postpartum care

It is important to note that there are significant differences in the postpartum care of women with HDP compared with women without. Newer data from 14 RCTs informed these updated recommendations.

The routine use of non‐steroidal anti‐inflammatory drugs in postpartum pain management in women with preeclampsia is conditionally recommended against until more data on safety are available (2C). The short term use of loop diuretics in the in‐patient setting can be considered where clinically indicated (ie, pulmonary oedema, clinical features of fluid overload) (2C).

There remain inadequate data to suggest the superiority of a single agent or group of agents in managing hypertension postpartum. The antihypertensives used antenatally can be continued postpartum, although in addition, enalapril can be used in the postpartum period. The choice of antihypertensive should be made through a shared, informed decision‐making process, particularly in lactating women (2D). The group acknowledges that there are ongoing RCTs examining antihypertensives in the postpartum period and that the recommendation on the choice of antihypertensives is subject to review based on future updated data.

Part 8: long term postpartum care

It is increasingly evident that women who develop preeclampsia and gestational hypertension in pregnancy are at an increased long term risk of ischaemic heart disease, cerebrovascular disease, hypertension and renal disorders. At the time of publication, there remain limited data on appropriate postpartum interventions in reducing the long term metabolic and cardiovascular risks. The recommendations presented in Box 9 are practice points based on data and clinical practice that are current at the time of publication. The guideline includes a clinician checklist and patient infographic that can be used in counselling women on the importance of postpartum and long term follow‐up.11

Importantly, health care providers should assess for normalisation of abnormal clinical and biochemical findings that developed during the pregnancy (eg, proteinuria, liver function abnormalities, hypertension) (Practice point). Where normalisation does not occur by three to six months, further investigation may be required (Practice point). The working group are aware of ongoing RCTs on this topic and anticipates an update in the rating of current recommendations based on new data in the near future.

Conclusion

The SOMANZ hypertension in pregnancy guideline 2023 presents significant updates on evidence‐based recommendations for screening, prevention and management of HDP that has been developed to NHMRC's standards. We encourage users to refer to the main document of the guideline for in‐depth information on the recommendations made and for future updates on recommendations.11

Box 5 – Management of non‐acute/non‐severe hypertension in pregnancy

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IR = immediate release; SR = slow release. * Choice of agent should be individualised based on women's medical history and through and informed, shared decision‐making process. † Oxprenolol is no longer accessible in Australia and New Zealand. Where it remains available, a dose of 20–60 mg three times a day can be used. Oxprenolol should be avoided in women with a history of asthma or chronic airway limitation. ‡ Access and supply may be limited in certain parts of Australia and New Zealand.

Box 7 – Management of acute hypertension in pregnancy

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BP = blood pressure; IV = intravenous; PP = practice point. * Target BP should be individualised particularly in the presence of features of fetal compromise. † The most important consideration in choice of antihypertensive agent is that the unit has access and familiarity with that agent. Agents should be uptitrated as indicated in the first line section in this Box, and if target BP is not reached, second and third line treatment options should be employed. ‡ Supply and access may be limited in Australia and New Zealand. § Administration of IV agents should be followed by a 10–20 mL normal saline IV flush to ensure systemic circulation of the administered agent. ¶ 250 mL IV fluid preloading (normal saline 0.9%) should be considered to minimise the risk of hypotension (PP). ** Slower onset of action (up to two hours). Use can be individualised based on clinical setting (ie, in the absence of short‐acting agents).

Box 8 – Management of eclampsia

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1A = based on 1A quality evidence; IM = intramuscular; IV = intravenous; MgSO₄ = magnesium sulphate; PP = practice point. * This flow chart provides guidance based on the evidence at the time of which this guideline was developed. Management of eclampsia must be done in accordance with local protocol where applicable.11