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Getting pregnant may take longer for women with asthma, a new study from Denmark suggests.
Researchers analyzed information from more than 15,000 women in Denmark, including 950 who had asthma.
When asked whether they had ever spent more than a year trying to become pregnant, 27 percent of women with asthma said yes, compared to 21 percent of women without asthma.
Women were particularly likely to experience a delay in pregnancy if they had untreated asthma, or if they had asthma and were over age 30. [7 Ways Pregnant Women Affect Babies]
The link between asthma and a prolonged time to pregnancy held even after the researchers took into account factors that could affect pregnancy chances, such as the woman's age, body mass index and smoking status.
Overall, women with asthma had the same number of children as women without the condition, a finding that may be due, in part, to women with asthma having their first child at younger ages, said study researcher Dr. Elisabeth Juul Gade, of the Respiratory Research Unit at Bispebjerg University hospital in Copenhagen.
The reason why women with asthma generally took longer to become pregnant is not known.
It could be that women with asthma are not able to attempt pregnancy (through unprotected sex) as frequently as women without the condition, said Dr. Avner Hershlag, chief of the Center For Human Reproduction at North Shore University Hospital in Manhasset, N.Y., who was not involved in the study.
"If you have any major medical condition that really interferes with your daily life, it's bound to also affect your conception," or efforts to get pregnant, Hershlag said. "When someone is sick and asthmatic, their focus changes, from 'I'm going to get pregnant,' to 'I'm going to get better,'" Hershlag said.
When a woman is in stable condition and no longer having frequent attacks, she is healthier and her body may be better able to handle pregnancy, Hershlag said.
An earlier study of nearly half a million people found that women with asthma had about the same fertility rate (number of live births per 1,000 people) as those without asthma.
"Long term, there is absolutely no effect on fertility for patients with asthma," Hershlag said.
However, the researchers hypothesized that asthma could have an effect on the uterus, and thus, potentially impact fertility. At least one previous study found an increased risk of miscarriage among women with asthma.
The inflammation that's characteristic of asthma has been shown to affect organs other than those of the respiratory system, the researchers said. Such inflammation might alter the blood supply to the uterus, which could impair the ability of an egg to implant there, the researchers said.
Ultimately, more research is needed to determine the reason for the link between asthma and a prolonged time to pregnancy. The researchers are now carrying out such a study, and will ask women about lifestyle factors, to determine if they play a role, Gade said.
The study is published in today's (Nov. 14) issue of the European Respiratory Journal.