Asthma during pregnancy is a special case in the treatment and management of asthma. It is important both to control asthma and to enable the pregnant woman to pass through pregnancy to delivery, and to avoid the harm that medications may cause to the fetus. The National Asthma Education and Prevention Program (NAEPP) first developed guidelines for the treatment of asthma in pregnancy in 1993. the NAEPP established a joint fund in seven states in the United States to reduce the morbidity and mortality of asthma, including children, adolescents, and low-income individuals. The guidelines have been revised several times in the last decade or so, and were updated again in 2005 after summarizing the management and treatment experience of the last decade or so, providing important guidelines for the use of medications in asthma during pregnancy. The incidence of asthma during pregnancy is estimated to be 3.8-8.4%, with an increasing trend in recent years. Pregnancy combined with asthma accounts for about 0.3-1.3% of maternal cases. Fifty-five percent of female patients with a history of asthma will experience at least one acute asthma attack during pregnancy. The interaction between pregnancy and asthma is variable during pregnancy, with approximately 1/3 of patients having an exacerbation (mostly between the 24th and 36th weeks of pregnancy), 1/3 having an improvement, and 1/3 having essentially no change. Pregnancy can have an impact on asthma. It has been reported that asthma persists during pregnancy in 0.2% of patients and that 10% of pregnant women have an acute asthma attack after delivery, while most women with asthma return to pre-pregnancy levels 3 months after delivery. Patients who have had asthma during pregnancy will still have a recurrence of asthma attacks in subsequent pregnancies. The characteristics of the changes during pregnancy vary for different degrees of asthma The more severe asthma tends to worsen during pregnancy, while the milder asthma tends to stabilize or improve. There are many factors that can cause asthma to worsen during pregnancy. Pregnancy can lead to changes in maternal immune function which increases maternal susceptibility, such as conception of a female fetus, irrational use of medication, and in some cases, patients with severe asthma before pregnancy, all of which can lead to worsening asthma. The mechanisms underlying the changes in asthma status during pregnancy are not well understood. It has been reported in the literature that the presence of the fetus and placenta during pregnancy causes changes in the maternal immune system that are very similar to those described in patients with non-eosinophilic asthma in the non-pregnant state. The impact of asthma on pregnancy is also significant. It can lead to preterm delivery, failure to thrive, growth retardation, overdue delivery, and low birth weight babies. It can also affect pregnant women, leading to pre-eclampsia, gestational hypertension, toxemia of pregnancy, vaginal bleeding, and obstructed labor. Severe asthma attacks can even endanger the life of the pregnant woman and her fetus. Whenever possible, non-pharmacologic medications should be used to reduce the damage to the fetus and to avoid medications whose safety to the pregnant woman and fetus is uncertain. If the condition requires medication, the dose should be kept to the lowest possible level and administered by inhalation whenever possible, reducing oral or injectable medications. Uncontrolled asthma can be very harmful to the mother and fetus, so it is essential to use medications to control asthma during pregnancy. Uncontrolled asthma increases the complications of pregnancy (low birth weight and prematurity). Uncontrolled asthma is much more risky for pregnancy than asthma treatment medications. Commonly used drugs for asthma in pregnancy are anti-inflammatory drugs such as glucocorticoids, sodium cromoglycate and sodium nedolomide, leukotriene modulators and bronchodilators, like β2 agonists, theophyllines, and anticholinergics. 1, glucocorticoids Glucocorticoids should be given mainly by inhalation. Inhaled hormones can work locally in the airway and can significantly reduce the adverse effects of systemic medication. Budesonide is the most common and safe inhaled drug used during pregnancy. It is a class B drug with no obvious harm to humans. This type of drug is safe for application during pregnancy, and it is the first choice of inhaled hormone during pregnancy. Regular therapeutic doses have no adverse effects on the fetus. When inhaled doses reach 1.4 to 1.8 mg/d, there is a possibility of hypothalamic-pituitary-adrenal axis function suppression. The inhaled hormones fluticasone and beclomethasone dipropionate, which belong to class C, have not been ruled out as dangerous, and such drugs can be applied during pregnancy. Studies have shown that inhaled hormones can improve lung function and reduce acute asthma attacks during pregnancy. Numerous prospective studies have found no correlation between inhaled hormones and fetal congenital anomalies or other adverse events during pregnancy, and Murphy notes that maternal airway inflammation in asthma is associated with low fetal weight in women, which can be prevented by inhaled hormones. Clinically, approximately nearly 5% of patients with asthma during pregnancy require oral hormones. Short-term oral hormone administration rarely results in systemic adverse effects. Animal studies have confirmed that the use of high doses of oral hormones is associated with fetal cleft lip, cerebral edema and cranial development defects, but this has not been demonstrated in humans . Prednisone is the most commonly used oral hormone, and 87% of the drug in the blood is inactivated by the action of 11-dehydrogenase in the placenta before it enters the fetal circulation through the placenta, with little effect on the fetus. At present, it is believed that if prednisone ≤10 mg is taken daily during pregnancy, there are few adverse effects on pregnant women and fetuses. In severe cases, prednisone 30-40 mg can be taken daily for 3-7 d. The dose can be gradually reduced to every other day or once daily in a single dose, and gradually overtaken to inhaled hormone therapy. With long-term oral hormone administration, pregnant women may develop reduced glucose tolerance or diabetes mellitus, osteoporosis, hypertension and other related diseases. Recent prospective cohort studies with large samples suggest that oral hormone and theophylline use are the greatest risk factors for preterm delivery in pregnancy, while atopic substances cannot be a definite risk factor. The NAEPP states that the application of oral hormones in early pregnancy (first trimester) increases the incidence of cleft lip and palate in the fetus. The incidence of fetal cleft lip and palate in the general population is 0.1%. Pregnant women who take oral hormones early in pregnancy have a fetal cleft lip and palate incidence of up to 0.3%. The incidence of preeclampsia, preterm birth, and low birth weight babies may increase if hormones are used throughout pregnancy. Sodium cromoglycate and sodium nedolomide Sodium cromoglycate and sodium nedolomide play an anti-inflammatory role by inhibiting the degranulation of mast cells, while weakening the respiratory neuronal reflexes and having a certain inhibitory effect on the accumulation of eosinophils and neutrophils in the lung epithelium. Inhalation of its powder before exercise or exposure to allergens can prevent asthma attacks. Sodium cromoglycate is a class B drug that is used as a mast cell stabilizer during pregnancy, has less than 10% systemic absorption, and does not cross the placenta. The NAEPP also states that cromoglycate is a safe drug to use during pregnancy. The NIH document states that inhalation treatment with sodium cromoglycate or budesonide in pregnant women with persistent asthma is considered the first-line drug. 3. Leukotriene modulators Leukotriene modulators mainly include leukotriene receptor antagonists (montelukast and zalalostat) and 5-lipoxygenase inhibitors (zileuton). A clinical study completed in recent years looked at 2205 pregnant women with 873 cases of asthma, of which 9 cases were not found to be abnormal with leukotriene receptor antagonists.NAEPP notes that there is only very little evidence to confirm the use of leukotriene modulators for asthma during pregnancy. The FDA has also only approved the results of animal studies of leukotriene receptor antagonists. 4. β2 agonists β2 agonists are indicated for patients with various degrees of asthma during pregnancy and can be used as first-line medications for mild asthma. The commonly used clinical drugs are salbutamol (class C), terbutaline (class B), and pirbuterol (class C). The NAEPP has updated its guidelines to confirm the safety of β2 agonists in pregnancy through extensive animal testing and experience with pregnant asthmatics over more than a decade, and to confirm that two long-acting β2 agonists (salmeterol and formoterol) are also available for use during pregnancy, with the same pharmacology and toxicology as the short-acting β2 agonists agonists (salbutamol) are similar, except that their deposition time in the lungs is prolonged. Theophylline drugs exert their pharmacological effects by relaxing bronchial smooth muscle, stimulating the respiratory center, enhancing diaphragm movement, and anti-inflammatory. As a second-line drug, this class of drugs has a limited therapeutic concentration range. During pregnancy, the theophylline concentration in blood or urine must be monitored and the dose adjusted to avoid serious side effects due to decreased hepatic metabolism. Theophylline can cross the placental barrier and there is no significant difference between maternal and umbilical cord serum theophylline concentrations. Transient neonatal vomiting, tremor and tachycardia can occur at blood concentrations greater than 10ug/ml. Theophylline blood levels should be maintained at 5-15ug/ml in non-pregnant asthmatics and at 5-12ug/ml in pregnant women. theophylline clearance may decrease by 20%-35% during pregnancy, so blood levels should be closely monitored. Aminophylline in pregnant women may reduce the incidence of gestational hypertensive syndrome and low birth weight babies. However, it may increase the incidence of preterm delivery and preeclampsia. The updated NAEPP guidelines state that a large number of studies and experience confirm that the administration of extended-release theophylline (blood levels of 5 to 12ug/ml) during pregnancy is safe. In a double-blind controlled study comparing the effects of hormones and theophylline in pregnant women with asthma, the incidence of adverse events, discontinuation rates during the observation period, and pulmonary function FEV1 in the theophylline group.