Patient information: Pregnancy and asthma

Steven E Weinberger, MDMichael Schatz, MD, MS

UpToDate performs a continuous review of over 375 journals and other resources. Updates are added as important new information is published. The literature review for version 15.2 is current through April 2007; this topic was last changed on May 18, 2006. The next version of UpToDate (15.3) will be released in October 2007.
INTRODUCTION — Asthma is the most common condition affecting the lungs during pregnancy. At any given time, up to 8 percent of pregnant women have asthma.
It is normal to worry about how the changes of pregnancy will affect asthma and if asthma and its treatments will harm the baby. With good asthma therapy, most women can breathe easily, have a normal pregnancy, and deliver a healthy baby. Overall, the risk of poorly controlled asthma is much higher than the risk of taking medications to control asthma.
Asthma therapy during pregnancy is most successful when a woman receives regular medical care and follows her treatment plan closely. Before becoming pregnant, women with asthma should learn as much as they can about their condition and talk with their healthcare providers about asthma therapy during pregnancy.
SEVERITY OF SYMPTOMS — The effects of pregnancy on asthma vary from woman to woman. Unfortunately, it is difficult to predict the course that asthma will follow in individual women who become pregnant for the first time. During pregnancy, asthma worsens in one-third of women, improves in one-third, and remains stable in one-third.
Other patterns that have been observed include: Among women whose asthma worsens, worsening is most rapid between weeks 29 and 36 of pregnancy. Asthma is generally less severe during the last month of pregnancy. Labor and delivery are not usually associated with a worsening of asthma. Among women whose asthma improves, the improvement progresses gradually throughout pregnancy. The severity of asthma symptoms in a first pregnancy is often similar in subsequent pregnancies.
Factors affecting risk of attacks — The factors that increase or decrease the risk of asthma attacks during pregnancy are not entirely clear. The likelihood of these attacks is not constant throughout pregnancy; attacks seem to be most likely during weeks 17 through 24 of pregnancy (show figure 1). The cause for this pattern is unknown, but researchers suspect that women may stop using asthma-controlling drugs when they discover that they are pregnant, increasing their risk for attacks.
EFFECTS OF ASTHMA ON PREGNANCY AND BABY — Women who have asthma have a small increase in the risk for certain complications of pregnancy, although the reasons for this are unknown. Compared to women who do not have asthma, women with asthma are slightly more likely to develop high blood pressure and preeclampsia during pregnancy, to have a placental abnormality called placenta previa, to have a premature delivery, and to require a cesarean delivery. Women with asthma are also slightly more likely to have a baby that is small for its age.
However, the vast majority of women with asthma and their babies do NOT have any complications during pregnancy. Good control of asthma during pregnancy reduces the risk of complications.
ASTHMA THERAPY DURING PREGNANCY — Good asthma therapy is essential to ensuring the health of both the mother and the baby. Asthma therapy in pregnant women is very similar to asthma therapy in nonpregnant women. Therapy during pregnancy has several key components, which are most successful when used together:
Monitoring Mother's lung function — Normal lung function is important to a mother's health and to her baby's well-being. Lung function can be monitored in a healthcare provider's office or hospital, although home monitoring often provides important information when asthma symptoms worsen, typically during the night or upon awakening.
Pregnant women can monitor their lung function at home by using a simple device that measures the peak expiratory flow rate (PEFR). Depending on the frequency of attacks, a healthcare provider may recommend measuring this rate twice per day: once upon awakening and again 12 hours later. Decreasing flow rates usually signal a worsening of asthma and a need for more intensive therapy, even if the patient is feeling well. (See "Patient information: How to use a peak flow meter").
Lung function tests performed in the doctor's office are also useful for distinguishing the shortness of breath associated with a worsening of asthma from the normal shortness of breath that many women experience during pregnancy. Baby's well-being — A baby's well-being is carefully monitored during regular medical visits throughout pregnancy. These visits are particularly important for women who have asthma.
Avoiding triggers — Several simple steps can help control environmental factors that worsen asthma and trigger attacks. These include: Avoid exposure to specific allergens, especially pet dander (such as fur or feathers), house dust, and nonspecific irritants, such as tobacco smoke, dust, and pollutants Cover mattresses and pillows with special casings to avoid house dust mites. Avoid sleeping on upholstered furniture (eg, couches, recliners). Pregnant women should not smoke or permit smoking in their home.
(For more information about trigger avoidance, see "Patient information: Trigger avoidance in asthma").
Education — Learning about asthma enables people with this condition to better manage their symptoms, prevent attacks, and react when attacks do occur. This education can be particularly reassuring and useful during pregnancy. Asthma education usually teaches strategies for recognizing the signs and symptoms of asthma, avoiding factors that trigger attacks, correctly using asthma-controlling drugs, and developing an individualized treatment plan for acute attacks.
Drug therapy — With a few exceptions, the drug therapy for asthma during pregnancy is very similar to the drug therapy for asthma at other times during a person's life.
Safety of allergy-controlling drugs — It is difficult to prove that asthma-controlling drugs are completely safe during pregnancy, but evidence from the use of these drugs in pregnant women for many years suggests that most of them probably carry little or no risk for the mother or baby.
It is important to weigh the unknown (but likely small) risks of asthma-controlling drugs against the potentially serious harm of undertreated asthma. In most cases, undertreated asthma poses a far greater risk to both the mother and the baby than the use of asthma-controlling drugs.
Types of asthma drugs — There are many different types of asthma-controlling drugs, and the drug or drugs that your healthcare provider recommends will depend upon many factors. In general, inhaled drugs are usually recommended because there is limited body-wide effects in the mother and the baby. It may be necessary to adjust the type or dose of drugs during pregnancy to compensate for changes in metabolism and the severity of asthma. Bronchodilators — Bronchodilators rapidly relieve asthma symptoms by relaxing the airways. They include albuterol (Proventil®, Ventolin®), metaproterenol (Alupent®), terbutaline, and other drugs. Newer drugs, such as salmeterol (Serevent®) and formoterol (Foradil®), are longer-acting bronchodilators; these have been used less frequently during pregnancy, so assessment of potential risk to the unborn baby is more difficult.
Bronchodilators appear to be safe during pregnancy. One study showed that the babies of women who used these drugs during pregnancy had no increase in health problems when compared to the babies of mothers who did not. About 70 percent of these women used the bronchodilators during the first trimester of pregnancy (a particularly sensitive time in fetal development), further suggesting that these drugs are safe.
A healthcare provider may avoid giving bronchodilator pills near the time of delivery because they can weaken uterine contractions. Corticosteroids — Corticosteroids are used to treat many conditions in addition to asthma. Experience from their use in pregnant women suggests that these drugs are generally safe for both the mother and the baby. The corticosteroids include pills such as prednisone and inhaled drugs such as beclomethasone (Beclovent®, Vanceril®, and others), triamcinolone (Azmacort®), flunisolide (AeroBid®), budesonide (Pulmicort®), and fluticasone (Flovent®).
- Oral corticosteroids - Some studies have suggested that there may be an increased risk of cleft lip or cleft palate in the babies of mothers who took oral steroid medications during the first trimester of pregnancy, although these results are not definitive. Two studies found a slightly increased risk of premature delivery, and one study found a slightly increased risk of having a low birth weight baby. However, the researchers could not rule out the possibility that these effects were related to the severity of asthma and not to the use of the drug. In very rare cases, a mother's use of corticosteroids may cause adrenal insufficiency (poor function of the adrenal glands) in the baby at the time of birth, but this condition can be treated and resolves over time.
Women who use corticosteroid pills during pregnancy may be more likely to develop gestational diabetes and high blood pressure, but these conditions can be detected and managed with regular medical visits.
Any of the above risks are probably smaller than the risk of not treating severe asthma, which could be life-threatening for the mother and the baby.
- Inhaled corticosteroids - The information about inhaled corticosteroids is quite reassuring. A variety of inhaled corticosteroids have been used during pregnancy. Budesonide is thought to be one of the safest inhaled corticosteroids. Beclomethasone has also been used extensively during pregnancy. Theophylline — Theophylline (Slo-bid®, Theo-Dur®, and others) has been used for many years during pregnancy without any apparent complications, suggesting that it is safe during pregnancy. As examples, one study of 193 women who took theophylline during pregnancy found no increase in complications; another study found that the risk of stillbirth was no greater in women who took these drugs than in women who did not.
The physiologic changes of pregnancy alter the body's metabolism of theophylline, frequently requiring an adjustment of the dosage. Theophylline, like the beta agonist bronchodilators, can block uterine contractions when taken near delivery. It may also cause a rapid heart beat and fussiness in the baby at the time of delivery, but these effects are usually short-lived. Theophylline can worsen symptoms of heartburn and nausea in the mother; another medicine may be preferred if these symptoms occur.
Since the introduction of the inhaled corticosteroids, theophylline is used less often for asthma in general, including during pregnancy. Inhaled corticosteroids have been shown to be more effective and to cause fewer side effects than theophylline. Cromolyn sodium — There was no increase in birth defects or other pregnancy complications in one study of women who took cromolyn sodium during pregnancy. Although it appears to be a very safe drug, it is not as effective in controlling asthma as inhaled corticosteroids Drugs that affect the leukotriene pathway — Some drugs help control asthma by blocking the leukotriene pathway, which plays an important role in asthma. These drugs include zafirlukast (Accolate®), montelukast (Singulair®), and zileuton (Zyflo™). Studies in animals suggest that zafirlukast and montelukast do not cause birth defects when taken during pregnancy, but there are no studies on the safety of these drugs during pregnancy. Little is known about the safety of zileuton in pregnant women, but it does increase the risk of pregnancy complications in animals and is not generally recommended for use during pregnancy. Antihistamines — Although antihistamines are not used to directly treat asthma, they may be used to treat the allergies that often accompany asthma. These drugs include chlorpheniramine (Chlor-Trimeton® and others), loratadine (Claritin®), fexofenadine (Allegra®), and cetirizine (Zyrtec®). Studies in both animals and humans suggest that antihistamines cause no increase or only a very small increase in the risk for birth defects when taken during pregnancy. Of the currently available preparations, chlorpheniramine (which can be sedating), loratadine, or cetirizine are considered the antihistamines of choice for use during pregnancy. Decongestants — Decongestants are not used for the treatment of asthma, but they may be used to treat the symptoms of upper airway allergies. Pseudoephedrine (Sudafed®) is a decongestant that is commonly available. Most studies examining the safety of decongestants during pregnancy have been small, making it difficult to draw clear-cut conclusions. Until more information is available, it would probably be best to avoid the use of any oral decongestants during the first trimester of pregnancy. After the first trimester, the use of pseudoephedrine is thought to be safe in women without high blood pressure. Immunotherapy — Immunotherapy refers to regular injections (allergy shots) given to reduce a person's sensitivity to allergens. This therapy appears to be safe during pregnancy, although it carries a very small risk of a severe allergic reaction (anaphylaxis) in any patient, including pregnant women.
It is probably safe for women who are already receiving immunotherapy to continue receiving shots during pregnancy. Women who are not receiving immunotherapy at the time they become pregnant generally should not start immunotherapy until after delivery.
Labor, delivery, and the postpartum period — Pregnant women with asthma should discuss their labor and delivery plans with their healthcare provider. Asthma will affect a provider's choice of medications commonly used during labor, delivery, and the postpartum period.
Women with asthma can be treated with the drug oxytocin (Pitocin®) to induce labor and to control bleeding after delivery. During labor and delivery, epidural anesthesia is preferred over general anesthesia for women with asthma because epidural anesthesia reduces the demands on the lungs. If general anesthesia becomes necessary, doctors select specific general anesthetics that promote dilation of airways. The painkillers morphine and meperidine (Demerol®) are usually not recommended for women with asthma because these drugs can cause a release of histamine and worsen an asthma attack, but the painkillers butorphanol (Stadol®) or fentanyl (Sublimaze®) are safe and effective alternatives.
WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two patients are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.
This discussion will be updated as needed every four months on our web site (www.patients.uptodate.com). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.
A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable. National Library of Medicine
(www.nlm.nih.gov/medlineplus/healthtopics.html) American Lung Association
(www.lungusa.org) Canadian Lung Association
(www.lung.ca) American Academy of Allergy, Asthma, and Immunology
(www.aaaai.org/patients.stm) National Heart, Lung, and Blood Institute
(www.nhlbi.nih.gov/health/prof/lung/asthma/astpreg.htm)