The most widely used tocolytic drugs include beta agonists and nifedipine (which relax smooth muscles, including the uterus), and atosiban and indometacin (which inhibit hormones involved in labor), according to the study. -- Certain drugs used to delay preterm labor can cause serious complications in women, a European study finds. Atosiban was the most commonly used drug (42 percent), follo by nifedipine (34 percent), beta agonists (14 percent), and indometacin (8 percent). Doctors use tocolytic drugs to delay labor for up to 48 hours. However, the use of these drugs is controversial, because it's not clear whether tocolysis is safe for both mother and baby.

The researchers analyzed the rate of serious complications in 1,920 women treated with tocolytic drugs for preterm labor at 28 hospitals in the Netherlands and Belgium. In this way, they gain time to allow steroids to hasten fetal lung development.

These delays also enable the expectant mother to be transferred to a medical facility with a neonatal intensive care unit, according to background information in the study.

The overall incidence of adverse effects was 0.7 percent, but combined or single treatment with a beta agonist led to a higher incidence of serious drug.