Many studies have been carried out all over the world to help doctors decide which asthma medicines are “safest” in pregnancy. The single biggest risk to an asthmatic woman’s pregnancy is poor asthma control in the mother. Uncontrolled asthma is very harmful to the developing baby and can result in devastating complications for both mother and child. Complications of poor asthma control include pregnancy-induced hypertension, pre-eclampsia and eclampsia in the mother, preterm labor and premature birth, intrauterine growth retardation, and low birth weight babies, along with increased perinatal morbidity and mortality. Inadequate control of the mother’s asthma leads to a reduced oxygen supply to the developing baby (“maternal hypoxia”), as well as a decreased blood supply to the womb. All pulmonary specialists agree that they should treat their pregnant asthma patients with asthma medicines that are not only highly effective, but also as safe as possible for both mother and baby.
The FDA classifies all medicines approved since 1980 into one of five different categories. The FDA classification is based on studies of safety in pregnancy. The five categories are referred to as category A, B, C, D, and X (Table The FDA’s Classification of Medicines in Pregnancy). Category A is considered the very safest, while category X drugs are absolutely contraindicated under any circumstances. There are no asthma medicines classified as category A. Most medicines used in asthma treatment fall into category C, and several are classified in category B. All short-acting β2 agonist “rescue” inhaled bronchodilator medications, for example, are classified as category C, even though they have been in use for over two decades, and are widely viewed as very safe by the medical profession.
Table The FDA’s Classification of Medicines in Pregnancy
|Category A||Adequate and well-controlled studies in pregnant women have not shown an increased risk of fetal abnormalities.=> Controlled studies show no risk.|
|Category B||Animal studies have revealed no evidence of harm to the fetus, but there are no adequate and well-controlled studies in pregnant women.Or…
Studies in animals have shown an adverse effect on the animal fetus but adequate and well-controlled studies in pregnant women have failed to demonstrate a risk to the human fetus.
=> No evidence of risk in humans.
|Category C||Studies in animals have shown an adverse effect on the animal fetus and there are no adequate and well-controlled studies in pregnant women to assess risk to the human fetus.Or…
No animal studies of the medicine have been performed and there are no adequate and well-controlled studies in pregnant women to assess risk to the human fetus.
=> Risk cannot be ruled out.
|Category D||Studies, adequate and well-controlled, or observational, have demonstrated a risk to the fetus. Benefits of therapy with this category of medicine in pregnancy may outweigh the potential risk to the fetus.=> Positive evidence of risk.|
|Category X||Studies, adequate and well-controlled, or observational, in animals or humans have demonstrated positive evidence of fetal abnormalities. The use of the medicine is contraindicated in women who are pregnant or who may become pregnant.=> Contraindicated in pregnancy.|
They have not been shown to have adverse effects on the course of the pregnancy, and have not been shown to be harmful to the human fetus. All long acting β2 agonist inhaled bronchodilators are also category C medicines. The “C” classification for the β2 agonist group of inhalers reflects the absence of studies in pregnant women. One inhaled corticosteroid preparation, Pulmicort (budesonide), is category B; all other inhaled steroids are, as of this writing, labeled category C. The long-term inhaled “controller” medicines Intal(cromolyn) and Tilade (nedocromil) are category B, as are the leukotriene modifier tablets Singulair (montelukast sodium) and Acolade (zafirlukast). The new immunoglobulin E blocker Xolair (omalizumab) carries a category B rating. The theophylline medicines are all category C drugs.
Because both uncontrolled asthma and poorly controlled asthma in the mother have such serious consequences for her and her unborn child, the guiding principle for the treatment of asthma in pregnancy is to achieve optimal asthma control even if daily medication is required. It is crucial to normalize maternal lung function and ensure that the mother is not experiencing any symptoms of asthma. Pulmonologists take the point of view that any medicine that is required for optimal asthma treatment should be administered to a pregnant woman. For example, steroid bursts are used in the setting of pregnancy just as they are when a woman is not pregnant. As a rule of thumb, we would use category B medicines first, adding any required medicines that may fall into the C category (or even D), if needed to achieve good asthma control. If you are pregnant and have any questions or any concerns about the safety of the medicines you have been prescribed, you should consult with your treating physicians. Both your obstetrician and your asthma doctor have the expertise to counsel you and give advice that is best for you. Under no circumstances should you stop your prescribed asthma regimen or not follow the treatment plans recommended by your doctor.