Researchers in Denmark have found that women with asthma take longer to become pregnant compared to non-asthmatics. The results add to an emerging body of evidence showing that asthma affects fertility.

Asthma is one of the most common chronic diseases in women during their reproductive years, affecting up to eight percent of pregnancies. Although studies have shown that asthma inhalers are safe for pregnant women, almost 25 percent of women stop using their inhalers during pregnancy.

The Danish study was based on questionnaire results of over 15,000 female twins living in Denmark between the ages of 12–41 years, which included questions on asthma and fertility. Around six percent of respondents reported having a history of asthma.

The researchers from Bispebjerg University Hospital found that asthmatic women in their 20s had a six percent greater chance of having a prolonged time to conception (defined as over one year) compared to non-asthmatics. The results were even more pronounced for women over 30. However, the impact of asthma on time to conception decreased for women whose asthma was being treated.

'The time to pregnancy is significantly prolonged in asthmatic individuals even after adjusting basic variables such as BMI, age and smoking', wrote Dr Elisabeth Juul Gade, the lead author of the study.

Despite the prolonged time to pregnancy, the study found that the total number of children that women had was not connected to asthma. Women with asthma started having children at an earlier age in general.

Previous studies have shown that asthmatic women have a higher risk of giving birth to an underweight baby. However, this study is the first to show the influence of asthma on fertility during conception.

Adam Balen, professor of reproductive medicine at Leeds Teaching Hospitals and spokesman for the Royal College of Obstetricians and Gynaecologists told The Times: 'The advice would be that women with asthma should [control their asthma] and not delay child bearing'.

One explanation that the authors provide for their findings is that inflammation resulting from asthma could alter the blood supply to the uterus, which could impair implantation or even lead to the rejection of a fertilised egg.

Deborah Waddell of Asthma UK told The Daily Mail that, 'Good asthma management is vital for the health of both mother and baby, and mums-to-be should continue to use their medication during pregnancy'.

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.