Asthma in Pregnancy

Asthmatics get pregnant, and of those who do approximately a third will worsen, a third will stay the same and a third will improve. Changes in severity usually occur during weeks 20-36.

Pregnant patients experience an increase in Tidal Volume and consequently a Respiratory Alkalosis . This alkalosis shifts the fetal oxygen dissociation curve to the left, reducing oxygen release. It also causes placental vasoconstriction. Couple this with maternal anemia and relative hypoxia secondary to asthma, and you can see the negative affect it can have on the fetus.

Uncontrolled asthma is associated with an increased incidence of abortion, premature labor, perinatal morbidity and mortality.

Inhaled bronchodilators are safe to use in pregnancy in the usual doses. In fact the patient should follow her usual treatment regime with respect to the management of her asthma.

The beta2-agonists can prolong labor and produce a fetal tachycardia as can Atrovent. Atrovent can also inhibit lactation.

Cromoglycate and betamethasone are safely inhaled during pregnancy. Oral steroids can be used as necessary, but one should consider covering the patient with methylprednisolone during delivery if the woman is on long term systemic steroids. One must also monitor for gestational diabetes in patients on systemic steroids.

A reasonable approach to asthma management for pregnant patients would be:

• Avoidance of known inducers of wheezing e.g. tobacco smoke
  
• Beta2-agonists on a PRN basis for wheezing
  
• Nedocromil sodium used prophylactically or prior to exposure to a known trigger.
  
• Addition of low dose inhaled steroids (e.g. beclomethasone 250-500 microgm. daily), if the frequency of beta2-agonist use is greater than 2- 4 times a day, or if nocturnal symptoms are present.
  
• Increase to high dose inhaled steroids (e.g. beclomethasone 1000-2000 microgm./day in divided doses) if the patient still needs her beta2 agonist more than 4 times a day, or if nocturnal symptoms are present.
  

If symptoms are still not abating, than oral steroids are required.

There are several regimes used. Some recommend 50mg. of prednisone (single tablet) for 5-7 days and then stop. Others recommend tapering off over 1-2 weeks.

Failure to respond by this time necessitates hospitalization and IV steroids.

- John Hickey