How to manage asthma in pregnancy

Continuing our series on complex asthma cases, respiratory specialists Dr Anna Haley and Dr Nita Sehgal discuss the key principles in management of asthma during pregnancy

What are the implications of poorly controlled asthma in pregnancy?

Asthma is the most common chronic health condition in pregnancy and is estimated to affect 8% of pregnant women in the UK.¹ Poorly controlled asthma increases the risk of both foetal complications including intra-uterine growth restriction, low birth weight and pre-term labour and maternal complications including pre-eclampsia and gestational diabetes. Systemic inflammation is hypothesised to be the most significant factor driving these observed poor outcomes as when asthma is actively managed and well-controlled, the risk of peri-natal complications is greatly reduced.²

How does pregnancy affect respiratory physiology?

Pregnancy increases oxygen demand and tidal volume from early in pregnancy, with a decrease in functional residual reserve in the third trimester due to elevation of the diaphragm. This may lead to a sensation of shortness of breath but is not typically associated with chest tightness or wheeze. Pregnancy does not significantly alter oxygen saturations, respiratory rate, peak flow, forced expiratory volume in 1 second (FEV1) or forced vital capacity (FVC). Therefore, when assessing a pregnant patient’s breathing, observational measures should be interpreted and acted upon as if they were not pregnant.

What are the effects of pregnancy on asthma?

Historical dogma describes a ‘rule of thirds’ about the effect of pregnancy on asthma, whereby pregnancy will cause asthma control to improve, stay the same or worsen in one third of women, respectively.

While this can be a useful guide, it is unlikely to accurately represent a woman’s individual risk of asthma control changing through her pregnancy, as many factors are thought to have an impact. The three variables with the strongest association with change in antenatal asthma control are:

Hormonal influences – rates of deterioration are low in the first trimester, while the highest exacerbation rates occur at 25-32 weeks gestation.³ Interestingly, exacerbations are less likely to occur in the last four weeks of pregnancy and are very rare during labour due to endogenous steroid release. Women are likely to experience similar changes to their asthma control in subsequent pregnancies.
Asthma severity prior to conception – this is a significant risk factor for deterioration in control, with patients with more severe asthma pre-conception more likely to deteriorate. Study data show exacerbation and subsequent hospitalisation rates in mild asthmatics who became pregnant are 13% and 2%, respectively, compared with 52% and 27% in those with severe asthma.⁴
Patients’ anxiety of potential foetal harm due to medication use, resulting in poor adherence – this is the biggest risk factor for uncontrolled asthma and subsequently poor outcomes. This is the most easily modifiable factor and highlights the important role of healthcare professionals in emphasising the safety of asthma medications with women prior to conception and early in their pregnancy (see below for discussion of medications in pregnancy).

How do you assess asthma severity in pregnant women?

Due to the propensity for asthma control to change in pregnancy, assessment of current day-to-day asthma control is important to pro-actively prevent exacerbations, and timely regular review should be provided throughout the pregnancy for those who do not have well-controlled symptoms.

Detailed asthma control scores such as ACQ-6 are very useful but are burdensome in a time-constrained primary care consultation. As a practical alternative, the Global Initiative for Asthma (GINA) recommends using four questions as an initial assessment of day-to-day asthma control (see Table 1).

In the last 4 weeks have you had any of the following?	Well controlled	Partly controlled	Poorly controlled
>2 episodes/week of daytime symptoms?	0 items	1-2 items	3-4 items
Limitation of activity due to asthma?
>2 episodes/week needing to use reliever?
Any night waking due to asthma?

Table 1. Screening questions to assess asthma control in the last four weeks.⁵

Alongside poor day-to-day asthma control, the following clinical patterns are most strongly associated with increased exacerbation risk:

Short-acting beta-agonist (SABA) overuse (three or more inhalers in one year equates to more than daily use).
Previous exacerbations requiring oral corticosteroids (OCS); particularly having a severe exacerbation requiring hospitalisation in the last year or previous intensive care admission.

If available, FeNO and blood eosinophils are useful biomarkers to assess and monitor airway inflammation that is likely to be steroid responsive in asthma.

What are the principles of education about asthma in pregnancy?

As per BTS/NICE/SIGN guidelines, women with asthma should have a review of their asthma during early pregnancy and in the postpartum period with an emphasis on the importance of continuing usual asthma medications to maintain good control.⁶

Other important factors in an asthma review of a pregnant patient include highlighting the importance of:

Smoking cessation and avoiding second hand smoking in the household. Though current evidence suggests vaping/e-cigarettes are much less harmful than smoking, they still contain some potentially harmful chemicals and women who vape should also be referred for support in quitting, with more information available via the NHS ‘Stop smoking in pregnancy’ website.⁷
Avoiding asthma triggers (ask about environmental and occupational exposure).
Vaccinations including influenza targeted at protecting pregnant mothers, and RSV (at 28 weeks) and whooping cough, (between 16 and 32 weeks), targeted at protecting baby.

What should a review of a pregnant patient’s asthma treatment include?

Consider whether inhaled therapy is in line with latest national guidance focusing on anti-inflammatory reliever (AIR) and maintenance and reliever therapy (MART).⁶
Formation of an up-to-date personalised asthma action plan.
Assessment of inhaler technique.
Review of adherence to preventer therapy with steps taken to address patients with <80% preventer pick-up or three or more salbutamol prescriptions in 12 months.
Provide reassurance on the safety of continuing their asthma medication and maintaining good control to reduce the risk of exacerbations and adverse outcomes, as outlined in the table below.

Asthma medication	Drug safety
Short-acting beta-agonists	Safe to use, no identified risk
Inhaled corticosteroids (ICS)	– No risk identified at normal prescribed dose – If initiating ICS: budesonide or beclomethasone preferred given largest evidence base – If asthma is controlled on alternate ICS pre-pregnancy: continue
Long-acting beta agonists (LABA)	– No risk identified in the available data – If initiating LABA (with ICS): salmeterol or formoterol preferred given largest evidence base – If asthma is controlled on alternate LABA (with ICS) pre-pregnancy: continue
Long-acting muscarinic antagonists (LAMA)	– Safety data in pregnancy is limited – Need individualised risk assessment – continue if it has led to improved control prior to pregnancy
Leukotriene receptor antagonists	– Safety data in pregnancy is limited – Montelukast preferred as most evidence – Continue if it has led to improved asthma control prior to pregnancy
Oral corticosteroids (OCS)	– Prednisolone is the preferred drug of choice as placental transfer to the foetus is low, (approximately 10%) compared to dexamethasone (33%) or hydrocortisone (15%) – Limited conflicting data describes associations between first trimester OCS use and a slightly increased risk of oral clefts, as well as later pregnancy use and low birth weight/preterm birth (latter may be confounded by asthma severity) – OCS are still considered to be safe and should be used as normal when clinically indicated for asthma exacerbations during pregnancy as poorly controlled asthma is strongly associated with worse foetal outcomes – Multiple courses of OCS are associated with an increased risk of gestational diabetes and pregnancy-induced hypertension; >1 course should prompt referral to a specialist asthma service

Table 2. Summary of drug safety information in commonly used asthma treatments in primary care

Patients who are prescribed specialist asthma medications should be reviewed by their prescribing respiratory physician early in pregnancy to make treatment decisions. Monoclonal antibody (biologic) therapies have preliminary pregnancy safety data that is encouraging, with the most evidence for omalizumab. A recent international expert consensus advised biologics can be initiated and continued in pregnancy following shared clinical decision making with patients.⁸

The UK Tetralogy Information Service is a great resource for clinicians on medicine safety information in pregnancy.⁹ You can also signpost patients to the Best use of medicines in pregnancy (BUMPS) website for ‘quick read’ patient information.¹⁰

When do you refer to an asthma service?

Referral to asthma specialist teams is indicated if pregnant patients have any of the following:

Poorly controlled asthma (e.g. GINA score >2 or ACQ-score >1.5) despite good adherence to therapy.
Asthma exacerbations requiring more than one course of OCS or a hospitalisation.
Any concerns from the patient or GP about their asthma control.

Referrals should be marked as urgent and triaged by secondary care for high priority review given the time-critical nature of antenatal asthma control. If advice and guidance is available, then this can be an effective way of optimisation prior to in-person review.

All women with severe asthma should be under the care of both severe asthma and maternal medicine/obstetric services.

How do you treat an acute asthma exacerbation in pregnancy?

It is important to treat acute asthma exacerbations as in non-pregnant patients to avoid adverse maternal-foetal outcomes. Prednisolone 40mg OD for 5 days is recommended if clinically indicated (see table above). Those with severe symptoms or not improving with this treatment should be referred for hospital assessment. In secondary care, for patients with severe exacerbations not responsive to initial therapy, both magnesium (which has good evidence of safety) and IV theophylline (which requires extra foetal monitoring for tachycardia when used in the third trimester) can be used.

Key points

Poorly controlled asthma is associated with maternal-foetal complications including pre-eclampsia, gestational diabetes, intra-uterine growth restriction, low birth weight and pre-term labour.
Asthma control can change during pregnancy and is highest risk of deteriorating between 26-32 weeks gestation and in those with severe asthma.
Asthma reviews should be conducted during early pregnancy to risk-stratify patients at risk of deterioration and educate patients on the non-pharmacological steps to help protect themselves and their baby.
GPs should pay particular attention to reassuring patients about the safety of asthma medication in pregnancy and the role of good adherence in preventing adverse maternal-foetal outcomes due to poor asthma control.

Dr Anna Haley is a respiratory registrar and Dr Nita Sehgal is a consultant in respiratory medicine at North Manchester General Hospital (Manchester University NHS Foundation Trust)

References

Charlton R et al. Asthma management in pregnancy. PLoS One. 2013;8(4):1-10
Murphy V et al. A meta-analysis of adverse perinatal outcomes in women with asthma. BJOG. 2011;118(11):1314-23
Murphy V et al. Asthma in pregnancy. Clin Chest Med. 2011; 32(1): 93-110
Schatz M et al. Asthma morbidity during pregnancy can be predicted by severity classification. J Allergy Clin Immunol. 2003;112:283-288
Global Initiative for Asthma (GINA). Pocket guide for asthma management and prevention for adults, adolescents and children 6-11 years. Global Initiative for Asthma. 2023:1-56
BTS/NICE/ SIGN. Asthma diagnosis, monitoring and chronic asthma management (NG245). NICE. 2024:1-64
NHS. Stop smoking in pregnancy. Last reviewed 2023
Naftel J et al. An international consensus on the use of asthma biologics in pregnancy. Lancet Respir Med. 2025;13(1):80-91
UK Teratology Information Service. Available at: uktis.org/
UKTIS. Bumps (Best use of medicines in pregnancy). Available at: medicinesinpregnancy.org/