Hypertension and pre-eclampsia

• Asthma is a risk factor for the development of gestational hypertension and pre-eclampsia in pregnancy, with exacerbations during pregnancy further increasing this risk.
• Pre-eclampsia is also a risk factor for the development of asthma in offspring
• All women should be assessed in early in pregnancy for clinical risk factors for pre-eclampsia.
• Blood pressure should be assessed at a women’s first antenatal visit to identify existing high blood pressure, and routinely measured to identify new onset hypertension.
• Managing asthma well during pregnancy is likely to reduce the risk of gestational hypertension and pre-eclampsia, however further research is needed.

For detailed assessment guidelines please visit the Society of Obstetric Medicine of Australia and New Zealand Guideline for the Management of Hypertensive Disorders of Pregnancy (2014, updated June 2015) (currently being updated).

Pregnant women with asthma are at increased risk of developing gestational hypertension and pre-eclampsia, with a recent study reporting an adjusted odds ratio of 1.29 (95% CI 1.26, 1.30) for either condition (Friedman et al. 2022).  

Earlier meta-analyses demonstrated a 54% increase in the relative risk of pre-eclampsia for women with asthma compared to women without asthma (RR 1.54, 95% CI 1.32, 1.81, 15 cohort studies)(Murphy et al. 2011).  Six studies adjusted for co-variates, and a meta-analysis of these confirmed the effect size and significantly elevated odds for pre-eclampsia among pregnant women with asthma (OR 1.57, 95% CI 1.24, 1.98)(Murphy et al. 2011).  

A recent Canadian population-based cohort study of over 103,000 pregnancies in 58,000 women with asthma (4.3% of pregnancies with an exacerbation) showed that exacerbations in pregnancy were associated with significantly increased odds of both gestational hypertension (OR 1.17, 95% CI 1.02, 1.33) and pre-eclampsia (OR 1.30, 95% CI 1.12, 1.51), after adjusting for potential confounders (Abdullah et al. 2020).  

In a Danish prospective cohort having an exacerbation was associated with a higher risk of severe pre-eclampsia compared to people without exacerbations, although this did not quite reach statistical significance (aOR 3.33, 95% CI 0.96, 11.65)(Ali et al. 2016).  

A sub-study of the Vitamin D Antenatal Asthma Reduction Trial (VDAART) found that uncontrolled asthma during pregnancy was associated with 3.55 times greater odds of pre-eclampsia (95% CI 1.15, 13.0), when the mother’s early pregnancy vitamin D concentration was controlled for (Mirzakhani et al. 2019).  Conversely, when asthma control status was controlled for, a 10ng/ml increase in maternal 25(OH)D levels was associated with a 7% reduction in risk of pre-eclampsia (Mirzakhani et al. 2019). 

Pre-eclampsia is a risk factor for the development of asthma in offspring, and mothers with asthma are more likely to have pre-eclampsia.  Pre-eclampsia is  also a risk for the future development of chronic hypertension, ischaemic heart disease, cerebrovascular disease, kidney disease and diabetes mellitus.

To investigate the potentially additive effects on asthma risk in early childhood, data from the Vitamin D Antenatal Asthma Reduction Trial (VDAART) were used (Mirzakhani et al. 2019a, 2019b).

• Children whose mothers had pre-eclampsia were at higher risk of asthma at age 6 years, compared to those whose mothers did not have pre-eclampsia (RR 1.71, 95% CI 1.10, 2.70).
• When mothers had asthma during pregnancy, children were 2.3 times more likely to have asthma diagnosis at age 6 years, compared to those whose mothers did not have asthma (RR 2.30, 95% CI 1.64, 3.23). When maternal risk factors were combined, there was an increasing incidence of asthma at age 6 years among children whose mothers did not have asthma or pre-eclampsia (6.7%), to those with mothers with pre-eclampsia but not asthma (14.3%), to those with mothers with asthma but not pre-eclampsia (16.2%) with the highest incidence observed when mothers had both asthma and pre-eclampsia (23.1%, OR 4.17, P<0.0001 for trend) (Mirzakhani et al. 2019b). This trend remained significant after adjustment for confounders, demonstrating the additive effect of maternal asthma and pre-eclampsia as risk factors for early childhood wheeze and asthma.   

• Measure blood pressure at a women’s first antenatal visit to identify existing high blood pressure, and routinely measure blood pressure at each antenatal visit to identify new onset hypertension.
• Early in pregnancy, assess all women for clinical risk factors for pre-eclampsia (i.e. history of pre-eclampsia, chronic hypertension, pre-existing diabetes, asthma, autoimmune diseases (such as systemic lupus erythematosus antiphospholipid syndrome), nulliparity, BMI>30, pre-existing kidney disease, asthma, and family history of pre-eclampsia (maternal pre-eclampsia or mother of the father of the current pregnancy).
• Routinely offer testing for proteinuria at the first antenatal visit, regardless of stage of pregnancy, using automated analyser if available. Recommend testing for proteinuria at each antenatal visit if a woman has risk factors for or clinical indications of pre-eclampsia, in particular, raised blood pressure.
• Any woman presenting with new hypertension after 20 weeks gestation should be assessed for signs and symptoms of pre-eclampsia.
• Women with asthma should undergo regular monitoring of clinical symptoms, with an asthma review every 4 weeks. See Toolkit section ‘Asthma management goals’ .

• Women presenting for antenatal care currently on medication for hypertension should have their medicines reviewed to ensure their safety in pregnancy.
• Advise women at moderate–high risk of pre-eclampsia that low-dose aspirin from early pregnancy may be of benefit in its prevention visit our page ‘Aspirin use for Obstetric indications’.
• Advise women at high risk of developing pre-eclampsia that calcium supplementation is beneficial if dietary intake is low. Advise on calcium rich foods.
• Give women information about the urgency of seeking advice from a health professional if they experience: headache, visual disturbance (such as blurring or flashing before the eyes), epigastric pain (just below the ribs), vomiting and/or rapid swelling of the face, hands or feet.
• It is important to recognise that women who have been diagnosed with either pre-eclampsia or gestational hypertension are at increased risk of subsequent hypertension and cardiovascular disease. For further information, visit: https://www.heartfoundation.org.au/Conditions/fp-pregnancy-and-heart-disease

General advice and recommendations adapted from: https://www.health.gov.au/sites/default/files/documents/2021/11/pregnancy-care-guidelines-pregnancy-care-guidelines.pdf