Women with asthma who suffer severe symptoms while they are pregnant face higher risks of health problems both for themselves and their babies compared to women with well-controlled asthma, according to research published in the European Respiratory Journal .
The study, which included data on more than 100,000 pregnancies, showed that women with asthma who experienced severe symptoms were more likely to suffer with high blood pressure (known as pregnancy-induced hypertension) and a potentially serious condition called pre-eclampsia.
It also showed that babies born to women who suffered asthma attacks were at greater risk of having a low birth weight, or being born prematurely or with a congenital abnormality, such as a heart defect or cleft lip. The children's risk of having asthma and pneumonia was also higher in the first five years of life.
The researchers say these findings are important because a large proportion of women with asthma are known to decrease or stop taking asthma medication during pregnancy.
The research was led by Dr Kawsari Abdullah, currently a research fellow at the Children's Hospital of Eastern Ontario, Research Institute in Ottawa, Canada. While conducting the study, Dr Abdullah was working at The Hospital for Sick Children (SickKids) in the Child Health Evaluative Sciences (CHES) Program, in Toronto.
She said: "Asthma is the most common chronic disease in pregnant women, affecting 8-13% of pregnant women worldwide.
"If asthma is poorly controlled, patients can suffer with severe symptoms such as wheezing, coughing, or feeling breathless or tight-chested. Previous research has shown that one out of every three pregnant women with asthma will suffer severe symptoms, so we need to understand what this means for women and their babies."
Dr Abdullah and her colleagues studied 103,424 pregnancies in 58,524 women with asthma living in the province of Ontario in Canada between April 2003 and March 2012. This included 4,455 pregnancies in 2,663 women who experienced severe symptoms while pregnant. This means they either visited their doctor at least five times because of their asthma symptoms, or went to the emergency department or were admitted to hospital at least once for asthma during pregnancy.
The researchers took account of other factors that can influence the health of the mother and baby, including the mother's age, whether she had been pregnant before, whether she smoked and her socioeconomic status.
They compared pregnant women with asthma who had experienced severe symptoms with pregnant women whose asthma was well-controlled. They found that those who had asthma attacks were around 30% more likely to suffer with pre-eclampsia and around 17% more likely to suffer with high blood pressure during pregnancy.
The results showed that babies born to mothers who had asthma attacks while pregnant were around 14% more likely to have a low birth weight, also around 14% more likely to be born prematurely, and around 21% more likely to have a congenital abnormality.
Children's risk of asthma up to the age of five years was 23% higher if their mother had experienced severe asthma symptoms in pregnancy, and their risk of pneumonia was around 12% higher.
Dr Teresa To, the senior researcher on the study and Senior Scientist at SickKids, said: "This is the biggest study looking at the risks associated with severe asthma symptoms in pregnancy and it's also the first to show the longer-term impacts on children up to the age of five years. Our results reinforce the findings of smaller studies that uncontrolled asthma can be bad for mothers and their babies.
"Nearly 40% of pregnant women decrease or stop taking asthma medication because they are worried that it could be harmful to their unborn babies. However, our study indicates that severe asthma symptoms present the greater risk to mother and baby.
"This study does not explain why asthma attacks contribute to all these health issues, but the likely mechanism is reduced oxygen supply for the mother and subsequently to the baby in the womb."
Professor Jørgen Vestbo is Chair of the European Respiratory Society's Advocacy Council, based at the University of Manchester and was not involved in the study. He said: "This large and important study suggests that asthma that is not well controlled may have serious effects on pregnant women and their children. This highlights the importance of carefully maintaining asthma control and managing asthma symptoms during pregnancy. Pregnant women who have asthma need regular antenatal care to discuss their symptoms and ensure their medication is effective."