© Springer India 2016
Alpesh Gandhi, Narendra Malhotra, Jaideep Malhotra, Nidhi Gupta and Neharika Malhotra Bora (eds.)Principles of Critical Care in Obstetrics10.1007/978-81-322-2686-4_11. Bronchial Asthma in Pregnancy
(1)
B.J. Government Medical College, Pune, India
The majority of women with asthma have normal pregnancies and the risk of complications is small in those with well-controlled asthma.
Asthma is estimated to occur in about 4 % of pregnancies, typically occurring as a pre-existing comorbidity, although some cases of asthma may initially present during pregnancy. The overall management goals of asthma in pregnancy are effective management of symptoms to avoid foetal hypoxia, whilst at the same time minimising any drug-related risks to the foetus [1].
The diagnosis of asthma is based on history, physical examinations and pulmonary function tests. The common symptoms are episodic breathlessness, wheezing cough and chest tightness. Episodic symptoms after incidental allergen exposure, seasonal variability of symptoms and a positive family history of asthma are also helpful diagnostic guides. The most usual physical finding is wheezing on auscultation. Pulmonary function tests like PEFR measurement with the help of a simple tool called peak flow meter can also aid in the diagnosis. The spirometric evaluation of asthma in pregnant patients is similar to that in non-pregnant patients. FVC, forced expiratory volume in 1 s into (FEV1), FEV1/FVC ratio and peak expiratory flow are stable to slightly increased in pregnancy [2].
Effect of Pregnancy on Asthma
Maternal hyperventilation occurs from increasing concentration of progesterone without a corresponding change in respiratory rate. Pregnancy has variable effects on asthma. About 28 % of pregnant asthmatics improve, 33 % remain unchanged and 35 % deteriorate usually between 24 and 36 weeks of gestation. Asthma symptoms improve during the last 4 weeks (37–40 weeks) [3].
During labour and delivery, only 10 % of asthmatics report symptoms and only half of those require treatment. During postpartum period, the severity of asthma reverts to its pre-pregnancy level. The conclusions of a meta-analysis of 14 studies are in agreement with the commonly quoted generalisation that during pregnancy about one third of asthma patients experience an improvement in their asthma, one third experience a worsening of symptoms and one third remain the same. There is also some evidence that the course of asthma is similar in successive pregnancies.
Studies suggest that 11–18 % of pregnant women with asthma will have at least one emergency department visit for acute asthma, and of these 62 % will require hospitalisation. Severe asthma is more likely to worsen during pregnancy than mild asthma, but some patients with very severe asthma may experience improvement, whilst symptoms may deteriorate in some patients with mild asthma.
A systematic review concluded that, if symptoms do worsen, this is most likely in the second and third trimesters, with the peak in the sixth month. In a large cohort study, the most severe symptoms were experienced by patients between the 24th and 36th week of pregnancy. Thereafter symptoms decreased significantly in the last 4 weeks, and 90 % had no asthma symptoms during labour or delivery [4].
Several physiological changes occur during pregnancy that could worsen or improve asthma, but it is not clear which, if any, are important in determining the course of asthma during pregnancy.
Pregnancy can affect the course of asthma and asthma and its treatment can affect pregnancy outcomes.
The following features may improve asthma during pregnancy:
Progesterone-mediated bronchodilatation
Oestrogen- or progesterone-mediated potentiation of beta-adrenergic bronchodilatation
Decreased plasma histamine-mediated bronchoconstriction
Pulmonary effect of increased serum-free cortisol
Glucocorticosteroid-mediated increased beta-adrenergic responsiveness
Prostaglandin E-mediated bronchodilatation
Atrial natriuretic factor-induced bronchodilatation
Increased half-life or decreased protein binding of endogenous or exogenous bronchodilator
Factors that may worsen asthma during pregnancy:
Pulmonary refractoriness to cortisol effects because of competitive binding to glucocorticoid receptors by progesterone, aldosterone or deoxycorticosterone
Prostaglandin F2a-mediated bronchoconstriction
Decreased functional residual capacity of the lung
Increased viral or bacterial respiratory infection-triggered asthma [5]
Increased gastrooesophageal reflux-induced asthma
Increased stress in pregnancy
Majority of effects are related to changing hormonal level in pregnant woman.
For example, the levels of free cortisol may improve asthma symptoms, whilst this effect may be counterbalanced by the pregnancy-related increase in serum progesterone, aldosterone and deoxycorticosterone.
In asthmatics with improved symptoms during pregnancy, the balance between these hormones may be tipped towards free cortisol, whilst the opposite occurs in those whose symptoms worsen. Improvement in symptoms during the last 4 weeks of pregnancy and the lack of symptoms during labour coincide with the highest level of free cortisol.
Effect of Asthma on Pregnancy Outcome
In most women asthma has no effect on the outcome of pregnancy. However uncontrolled asthma may lead to increase in preterm birth, low birth weight, neonatal seizure, transient tachypnoea of the newborn and neonatal hypoglycaemia. Uncontrolled asthma can also lead to higher rates of pregnancy-induced hypertension or pre-eclampsia and caesarean section, hyperglycaemia, vaginal haemorrhage and premature rupture of membranes [6].
The risks for preterm delivery and low birth weight were higher in women with more severe asthma necessitating admission. In a large cohort study of women with asthma, there was an association of both mean FEV1 and mean FEV1 <80 % predicted with gestational hypertension, preterm delivery <37 and <32 weeks and low birth weight.
In contrast, if asthma is well controlled throughout pregnancy, there is little or no increased risk of adverse maternal or foetal complications [7]. Pregnancy should therefore be an indication to optimise therapy and maximise lung function in order to reduce the risk of acute asthma attacks and hypoxia.
Monitoring of Asthmatic Women during Pregnancy
Monitor pregnant women with moderate/severe asthma closely to keep their asthma well controlled. Women should be advised of the importance of maintaining good control of their asthma during pregnancy to avoid problems for both the mother and baby
Office spirometry at each visit preferably at every 4–6 weeks.
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