Description
- Commonest chronic respiratory condition complicating pregnancy
- Course unpredictable: ~1/3 improve, 1/3 unchanged, 1/3 worsen ("rule of thirds")
- Severity tends to run true across trimesters of the same pregnancy and recur similarly in future pregnancies
Epidemiology
- ~12-13% of pregnant women in Australia
- Exacerbations commonest in 2nd trimester (weeks 24-36); rare in labour
Aetiopathogenesis
- Mechanical - diaphragm splinting by gravid uterus, dec functional residual capacity
- Physiological - progesterone-driven hyperventilation (normal in pregnancy) can mask/mimic dyspnoea of poor control
- Immunological shift may alter airway hyperresponsiveness (direction unpredictable per individual)
- Non-adherence from fear of medication harm is the single biggest driver of poor control - not the disease itself
Diagnosis
- Same criteria as non-pregnant - symptoms + spirometry/PEF, reversibility
- Distinguish from normal pregnancy dyspnoea: physiological dyspnoea is not associated with wheeze, cough, or reduced exercise tolerance and does not worsen progressively
- Assess control at every antenatal visit (validated tools e.g. ACQ) - do not rely on the woman volunteering symptoms
Management
Principle - management mirrors the non-pregnant patient
- Continued good control is safer for mother and fetus than any medication risk
- Do not step down or stop preventer therapy because of pregnancy
Medications - reassuring safety data
- ICS (budesonide most studied) - safe, continue
- SABA (salbutamol) - safe, continue as reliever
- LABA, montelukast, theophylline - continue if already required for control
- Oral corticosteroids - use when indicated for exacerbations; untreated severe asthma is more dangerous to the fetus than a steroid course
Monitoring
- Review every 4 weeks through pregnancy (more often if poorly controlled)
- Written asthma action plan updated for pregnancy
- Growth ultrasound surveillance if moderate-severe or poorly controlled asthma (risk of FGR)
Acute exacerbation
- Treat as for the non-pregnant patient - do not under-treat for fear of medications
- Maternal hypoxia is the primary threat to the fetus - supplemental O2 early, target SpO2 >=94-95%
- Continuous fetal monitoring if >=24 weeks and unwell
- Low threshold for hospital admission - deterioration can be rapid
Labour
- Continue usual medications through labour (including inhaled steroids)
- Prostaglandin F2-alpha (carboprost) for PPH is relatively contraindicated (bronchoconstriction) - use alternative uterotonics
- Avoid NSAIDs if aspirin/NSAID-sensitive asthma
Associations
- Poorly controlled asthma: pre-eclampsia, FGR, preterm birth, low birth weight
- Gestational diabetes (with recurrent oral corticosteroid courses)
- Well-controlled asthma: outcomes similar to the general obstetric population
Natural history & complications
- Postpartum - asthma control usually reverts to pre-pregnancy pattern within 3 months
- Course tends to recur similarly in subsequent pregnancies
- Breastfeeding safe with all standard asthma medications
7 of 7 sections written · drafted 2026-09-13