Asthma in Pregnancy

Etiology

The mechanisms, predictors, and outcomes of asthma exacerbations during pregnancy are not well understood. Many previous studies have shown that the bronchial asthma exacerbation rate in pregnancy is related to increasing asthma severity. Other studies considered nonadherence with bronchial asthma controller medication due to concern about its teratogenic effect during pregnancy to be an important risk factor for asthma exacerbations during pregnancy. Respiratory viral infections are also risk factors that trigger bronchial asthma exacerbations in pregnancy.[1][2]

Epidemiology

The prevalence of bronchial asthma during preg­nancy in the United States is between 8.4% and 8.8%. In other countries, the prevalence of bronchial asthma may be higher or lower, so further data is needed for demonstrating international trends. Bronchial asthma diagnosis may be different according to population characteristics.[1]

Pathophysiology

Many physiologic changes take place during pregnancy that can affect the bronchial asthma course including:

• A metabolic rate increase of the pregnant women by about 15%, with a resultant 20% increase in oxygen consumption with a subsequent increase in minute ventilation (mainly by tidal volume increase) by 30% to 40%.This hyperventilation is mediated by respiratory center stimulation by progesterone hormone. The hyperventilation leads to respiratory alkalosis during pregnancy, in which there is decreased arterial partial pressure of carbon dioxide, decreased bicarbonate, and increased pH.[3]
• Uterine size increases with its upward push on the diaphragm and a subsequent decrease in functional residual capacity.[3]
• The changes of maternal immunity as pregnancy are proposed to be associated with a shift from T-helper 1-type cytokine production and towards Th2-type immune responses, which is mandatory for the fetus to survive. The Th2 up-regulation and other immunity changes may lead to bronchial asthma exacerbation during pregnancy.[4]
• Mucosal and laryngeal edema may be mediated by the estrogen hormones leading to rhinosinusitis in about 20% of pregnant women.[5]

History and Physical

Approximately one-third of pregnant women suffer from a worsening of their bronchial asthma during pregnancy; in another one-third, asthma severity remains without change; while in the remaining third, their bronchial asthma shows improvement from the basal condition. The explanation of this variability still unexplained.[2]

Symptoms of asthma peak in the late second or early third trimester, but exacerbations are rare during labor and the peripartum period.[6]

Symptoms of bronchial asthma may include chest tightness, wheeze, shortness of breath, and cough. These symptoms are characterized by the following:

• Variability over time and in intensity
• Often are worse at night or in the early morning
• Symptoms are triggered by viral infections (colds), exercise, allergen exposure, changes in weather, laughter, or other irritants

Physical examination in people with bronchial asthma may be normal, but the most frequent physical sign is wheezing on auscultation. Wheezing may be absent in cases of severe bronchial asthma exacerbations as a result of severe reduction of airflow (silent chest).[6]

Evaluation

Like bronchial asthma in the general population, spirometry can help in bronchial asthma diagnosis in pregnancy by detecting reversible airway obstructive pattern and helping to monitor response to asthma treatment.

A methacholine challenge test is contraindicated during pregnancy as it may lead to acute bronchospasm.[7]

An asthma control test (ACT) can be used to assess bronchial asthma control during pregnancy. The ACT is five items, with a 4-week recall of symptoms and daily functioning (self-administered questionnaire). The scores range from 5, indicating poor asthma control, to 25 for complete control. A score of less than 20 on the ACT is defined as uncontrolled asthma.[8]

Bronchial asthma patients are considered to have bronchial asthma exacerbation if they have a change of the basal condition which leads to any of the following:

• Adding oral corticosteroids for BA treatment
• Unscheduled outpatient visits
• Admission to the emergency room or the need for hospitalization[7]

Treatment / Management

The goals of bronchial asthma treatment in pregnancy are to control asthma symptoms, maintain optimal lung function, and avoid bronchial asthma exacerbation in addition to maintaining fetal oxygenation by avoiding attacks of maternal hypoxia.

The National Asthma Education and Prevention Program recommends treating and managing bronchial asthma in pregnant women the same as in non-pregnant patients (Evidence B).

Salbutamol is the preferred reliever due to its high safety profile. Inhaled corticosteroids (ICS) are the preferred controller medications. It is safe to use ICS, theophylline, and montelukast during pregnancy. Prolonged use of systemic steroids has been associated with pregnancy-related complications, especially in the first trimester. But systemic steroids if indicated they should be used the same as in non-pregnancy (Evidence C). Research has suggested that management of asthma in pregnancy based on the fraction of exhaled nitric oxide (FENO) and symptoms significantly reduces asthma exacerbations.[9] In moderate-persistent asthma, a long-acting beta 2 agonist combined with an inhaled anti-inflammatory agent or inhaled corticosteroid is recommended for treatment. In severe asthma, oral corticosteroids and long-acting beta agonists are recommended. Inhaled glucocorticoids are relatively safe although there is a potential risk for endocrine and metabolic disturbances in fetuses. Sustained use of systemic steroids may increase the risk of congenital malformation, prematurity, neonatal insufficiency, low birth weight, preeclampsia, and gestational diabetes.[10] If anesthesia is indicated during labor, regional anesthesia is preferred.[11][7](A1)

Differential Diagnosis

The following should be considered in the differential diagnosis of bronchial asthma during pregnancy:

• Gastroesophageal reflux disease
• Postnasal drip
• Vocal cord dysfunction
• Hyperventilation syndrome
• Pulmonary embolism[12]

Prognosis

Uncontrolled asthma in pregnancy has been linked with a higher incidence of low fetal birth weight and preterm birth.[13] However, in general, the prognosis of asthma in pregnancy is similar to that of asthma in other populations. Patients who are pregnant and diagnosed with bronchial asthma should receive adequate asthma assessment and treatment. Bronchial asthma should be treated and managed in pregnant women the same as in nonpregnant patients. (Level II)

Complications

The complications of bronchial asthma in pregnancy are related to the severity and the intensity of treatment of bronchial asthma. Bronchial asthma exacerbations are considered the most important factor leading to maternal and fetal morbidity and mortality in pregnancies related to bronchial asthma. 

In fact, poorly controlled asthma has been associated with numerous adverse perinatal outcomes, including the following:

• Preeclampsia
• Pregnancy-induced hypertension
• Preterm labor and premature birth
• Congenital anomalies
• Low birth weight
• Neonatal hypoglycemia, seizures

Asthma can also lead to the following morbidities in pregnant women:

• Respiratory failure and the need for mechanical ventilation
• Barotrauma
• Complications of (parenteral) steroid use