A large Canadian study has reinforced the importance of controlling asthma in pregnancy, finding that exacerbations are associated with more complications for mother and baby and more childhood respiratory disease.
Using data from the Ontario asthma surveillance system and population-level health databases, a team led by Dr Kawsari Abdullah at the Hospital for Sick Children in Toronto analysed more than 100,000 pregnancies in women, all of whom had asthma.
Those who had exacerbations during their pregnancy (defined for the purpose of the study as five or more doctor visits, one emergency visit or one hospital admission for asthma) were more likely to suffer from pregnancy-induced hypertension (30% more likely) and pre-eclampsia (17%) than those who had no exacerbations.
Babies were more likely to have low birth weight (14%), be pre-term (14%) or have congenital malformations (21%).
As infants they were slightly more likely to develop asthma or a case of pneumonia before the age of five. Small increased risks of allergy and bronchiolitis were also found; these did not reach significance after adjusting for a long list of confounders including pre-term birth and maternal pre-eclampsia and hypertension.
The authors said the study was the first to use population-level data and that it measured the impact of asthma exacerbations, not just having asthma. They acknowledged, however, that their definition of an exacerbation, in the absence of a validated measure, brought a small chance of misclassification.
Dr Jonathan Burdon, a respiratory physician and past chair of the National Asthma Council, said while the headline message of the study was not new, it was a timely reminder to all health practitioners that asthma in pregnancy needed to be better managed.
As the study was so large, there was “strength in numbers”.
Dr Burdon said 30-40% of people who were prescribed regular long-term asthma medication did not take it as prescribed, and they were overrepresented in hospital admissions generally and in cases of thunderstorm asthma.
“So the message there [in general] is that if you’re prescribed regular medication there’s a good reason for it and please take it,” he said.
“The message I take from this paper is that people who have asthma and are pregnant should carefully manage their asthma and take the medication as recommended by their treating doctor, and I believe that regular review during pregnancy is sensible.
“I would see [pregnant patients] every six weeks or so, just as a routine, on the grounds that I may pick things getting worse before you do.
“And treat asthma flare-ups promptly: don’t wait and see if it’s going to go away tomorrow. The reasoning is that if you have a bad attack of asthma, the baby is one step down the oxygen supply line. If mum’s going to get a little bit hypoxaemic, the baby’s going to be more hypoxaemic.”
The paper says about 40% of pregnant women are known to stop taking their asthma medications, probably out of a misplaced fear that they will harm the fetus.
“The medical profession has trained our pregnant women very well: don’t smoke, don’t drink, don’t take drugs [pharmaceuticals],” Dr Burdon said. “I think once the women get pregnant, they say, I’d better stop taking my medication cause it’ll affect the baby.
“Oral steroids – prednisolone, dexamethasone et cetera – have been shown to result in a slightly higher risk of cleft palate and harelip in rats, but that hasn’t been seen, that I know of, in humans.
“And we very seldom use oral steroids unless someone’s really ill – if you need oral steroids there’s a really good reason for it. We need to get you fixed quickly, and I would always use a short course.
“More importantly, inhaled steroids and the inhaled bronchodilators like salbutamol and formoterol have not been shown to have any effect on the fetus.”
The study authors briefly entertain the idea that it could be asthma medications, including oral steroids, that are causing the adverse outcomes. But they quickly dismiss that as a less likely culprit than hypoxia from asthma exacerbations.
Dr Burdon said obstetricians and gynaecologists needed to insist their patients keep taking asthma medications as prescribed and reassure them that they were safe, and that women should also raise their pregnancy with their treating respiratory doctor.
European Respiratory Journal; online 26 November, 2019