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Disclaimer: This newsletter, provided by ITIS, is funded by a grant from the Illinois Department of Public Health and supported by Northwestern Memorial Hospital and Northwestern University Medical School. It is for educational purposes only and is meant to summarize the information available at the time of its creation. It should be construed neither as medical advice nor opinion on any specific clinical situation. For more information on a specific clinical situation,or updated information, please consult your health care provider. ASTHMA AND PREGNANCY Volume 9, Issue 2. February, 2002 Theresa Frezzo, BS, Carrie L. McMahon, MS, and Eugene Pergament, MD, PhD, FACMG Approximately 6 million women under the age of 45 are affected with asthma (1). It is estimated that 0.5-1.3% of all pregnancies are complicated by maternal asthma, making asthma one of the most common complications of pregnancy (2). The Effects of Pregnancy on Asthma Asthma symptoms vary in relation to the severity of the disease during pregnancy. Approximately 1/3 of asthmatic women report more severe symptoms during pregnancy than before. 1/3 report less symptoms, and 1/3 report their asthma symptoms remain unchanged during pregnancy. About 2/3 of all women report some dyspnea during pregnancy. Asthmatics enter pregnancy with preexisting problems limiting breathing and lung function. In all pregnant women, changes in function and capacity of the lungs, and pressure on the chest wall are attributed to the circumferential expansion of the uterus. Consequently, during pregnancy asthmatic women need to be particularly aware of their ability to inhale adequate amounts of air (3). Several theories have been postulated about the discrepancies between changes in asthmatic symptoms during pregnancy compared to preconception. There have been reports of individual women who experience improvement of symptoms with one pregnancy, and worsening of disease in their next. Beecroft et al (4) suggested that the sex of the fetus might influence the course of asthma during pregnancy. In a blind prospective study, they found that 50% of mothers of females reported increased asthmatic symptoms during pregnancy compared to 22.2% of mothers of males. Furthermore, mothers of males tended to report an improvement in their asthmatic symptoms (44.4%), while none of the mothers of females indicated any improvement. These researchers postulate that the adrenergic surge experienced by a woman while carrying a male fetus might mitigate her asthma. The Effects of Asthma on Pregnancy Asthmatic women are at an increased risk for several complications during pregnancy. Adverse fetal outcomes associated with asthma include pre-term delivery, low birth weight, small size for gestational age and increased length of hospital stay. The pregnant woman with asthma is at risk for experiencing preeclampsia, placenta previa, caesarian delivery and increased length of hospital stay (2). In pregnancy, the arterial blood gases are typically close to the following values: PO2 remains near 100 mm Hg, arterial pH increases to 7.40 to 7.45, and arterial PCO2 slightly decreases to 25 to 32 mm Hg. Hypoxia is the state when oxygenation of the arterial blood and tissues falls below normal. Status asthmaticus or severe asthmatic exacerbations can result in this dangerous state. A minimal change in maternal blood oxygen concentration may result in appreciable changes in fetal oxygen content. Fetal oxygen requirements increase exponentially with gestational age. The exact level of hypoxia that causes fetal death is unknown. A maternal PO2 <60 mm Hg portends fetal jeopardy. For these reasons, it is crucial for the asthmatic mother to realize that she is breathing for herself as well as he fetus (3). Relative maternal hypoxia has been shown to lower infant birth weight in otherwise normal pregnant women, e.g., women who live at a high altitude (5). Pulmonary function can be quantified by FEV1 (Forced Expiratory Volume during 1 second) and compared to a predictive value based on height and weight. Schatz et al (5) studied pulmonary function throughout pregnancy in 360 asthmatic women. They found a small, but statistically significant correlation between infant birth weight and average maternal FEV1, measured monthly throughout pregnancy: the lower the mother's pulmonary function, the lower the weight of her baby. Even when these clinicians controlled for smoking during pregnancy, this correlation remained significant (5). Controlling Asthma During Pregnancy The results from studies on the safety of asthma medications during pregnancy have been conflicting. It is difficult to determine if adverse pregnancy outcome(s) in an asthmatic woman is a result of the disease, or other confounding factors. Most studies conclude that asthmatic medications are non-teratogenic (6,7,8,). However, these conclusions are difficult to interpret because the study populations tend to be small. Common Asthma Medications Often asthma treatment involves the use of corticosteroid In general, the use of coricosteroids (inhaled and/or oral) during pregnancy has been associated with an increased risk for cleft lip, with or without cleft palate. A population study, carried out in Spain, examined 1,184 infants and found that maternal use of coricosteroids correlated with a 6-fold increase in risk for cleft lip, with or without cleft palate. Although this figure appears to represent a large increase in risk, there were, in fact, only 2 cases of oral clefting associated with corticosteroid exposure, compared tot he expected rate of 0.2 (8). At Northwestern University, 80 pregnancies with first trimester exposure to oral and/or inhaled corticosteroids were evaluated and 2 infants were found to have congenital malformations. There were no infants in this series born with an oral cleft; the malformations included one infant with a ventricular septal wall defect and the other with Down syndrome. Since the general population risk for birth defects is between 3-5%, the 2.5% of infants with congenital malformations in this study was well within the expected range. This study concluded that use of corticosteroids during pregnancy did not increase this risk (9). Most studies do not support a large teratogenic risk, however the association of corticosteroid use and clefting cannot be excluded. For more information regarding Corticosteroid Use in Pregnancy, please see RISK Newsletter Volume 8 No.1, April 2000. Several reviews of current literature have assessed the safety of common asthma medications during pregnancy (10,11). These will be briefly reviewed in the remainder of this newsletter.
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