Use of anti-asthmatic drugs during pregnancy. 1. Maternal characteristics, pregnancy and delivery complications.

Objective: To study, in a large cohort, the association between the use of anti-asthmatic drugs during pregnancy and pregnancy complications.

Methods: Using the Swedish Medical Birth Register, we identified 24,369 women who reported the use of anti-asthmatic drugs in early pregnancy and 7778 women who were prescribed such drugs later during pregnancy by antenatal care system centres, during the period July 1, 1995 up to and including 2004. We studied maternal characteristics and pregnancy and delivery complications. Comparisons were made with all women having given birth to a child recorded in the register during this period.

Results: Women using anti-asthmatic drugs were characterized by a young maternal age, low parity, increased rate of smoking, low education, and high body mass index. An association with subfertility was also observed. Pre-existing diabetes did not occur in excess. A number of pregnancy and delivery complications occurred at an increased rate with the use of anti-asthmatic drugs, notably when three or more such drugs had been used: gestational diabetes [odds ratio (OR)=1.59], preeclampsia (OR=1.44), haemorrhage at delivery (OR=1.32) and premature rupture of membranes (OR=1.59); no excess of placenta abruption or previa was found. Primary weak contractions occurred more often than expected in women that used anti-asthmatic drugs (OR=1.15), and this was tentatively linked to the use of beta-2 adrenergic agonists. Most of the increased risk for caesarean section (OR=1.79) could be explained by these pregnancy complications. An increased risk for delivery induction (OR=1.74) was found among deliveries that did not start with a caesarean section.

Conclusion: An increase risk of pregnancy complications occurs with the use of anti-asthmatic drugs by pregnant women, which results in an increased rate of caesarean sections.