Asthma in Pregnancy

Asthma in pregnancy is chronic airway inflammation with reversible airflow obstruction in a pregnant woman. It is triggered by allergens, infection, smoke and exercise. Poor control causes maternal hypoxia, preeclampsia, preterm birth and low birth weight, while well controlled asthma carries outcomes close to those of women without asthma.

• About one third of women improve, one third worsen and one third are unchanged; worsening is most common at 24 to 36 weeks.
• Risk factors: allergy, smoking, obesity, reflux, respiratory infection, stopping inhaled steroids on learning of the pregnancy.
• Inhaled drugs are safe; uncontrolled asthma is more dangerous than the drugs.

Women have cough, wheeze, breathlessness, chest tightness and night symptoms, which vary with triggers and time of day. Examine respiratory rate, wheeze, oxygen saturation and peak flow; the breathlessness of normal pregnancy does not wheeze and does not vary.

• Night cough and early morning symptoms.
• Reliever use more than twice a week signals poor control.
• Differential diagnosis: physiological breathlessness of pregnancy, pulmonary embolism, peripartum cardiomyopathy, pneumonia, reflux cough, anaemia, heart disease.
• Complications: acute exacerbation, hypoxia, preeclampsia, preterm birth, low birth weight, fetal growth restriction, caesarean birth, maternal death in severe attacks.

The diagnosis is clinical, supported by lung function.

• Peak flow variation above 20 percent between morning and evening, or a rise of 60 L/min after salbutamol.
• Spirometry: FEV1 to FVC ratio below 0.75 with reversibility of 12 percent and 200 mL after salbutamol.
• Oxygen saturation at each visit; full blood count to exclude anaemia; shielded chest X-ray only if pneumonia is suspected.
• Growth scan at 32 weeks if control is poor or steroids are needed.

The principle is to keep asthma controlled with stepwise inhaled drugs and treat exacerbations early.

• Supportive: avoid triggers; stop smoking; inhaler technique with a spacer; written action plan; twice daily peak flow chart with a target above 80 percent of personal best; treat reflux and rhinitis; influenza vaccine 0.5 mL IM in season.
• Pharmacological: reliever salbutamol 100 micrograms per puff, 2 to 4 puffs by spacer as needed; preventer beclometasone 100 to 200 micrograms inhaled twice daily (up to 800 micrograms daily) or budesonide 200 to 400 micrograms inhaled twice daily; step up by adding salmeterol 50 micrograms inhaled twice daily or montelukast 10 mg oral at night; for an exacerbation give prednisolone 40 mg oral daily for 5 to 7 days; in labour continue all inhalers, and give hydrocortisone 100 mg IV 6-hourly if the woman has taken prednisolone 10 mg or more daily for more than 2 weeks.
• Procedures: none.
• Special groups: for postpartum haemorrhage use oxytocin 10 IU IM and avoid carboprost, which causes bronchospasm; women sensitive to aspirin avoid ibuprofen and diclofenac; inhaled and oral asthma drugs are compatible with breastfeeding.
• Red flags: unable to complete sentences, respiratory rate above 25 per minute, pulse above 110 per minute, peak flow below 50 percent of best, oxygen saturation below 94 percent, reduced fetal movements.
• Follow-up: review every 4 to 6 weeks; step down after 3 months of good control; check inhaler use each visit; postnatal review at 6 weeks.