FRIDAY, March 6 (HealthDay News) -- Certain drugs used to delay preterm labor can cause serious complications in women, a European study finds.

Doctors use tocolytic drugs to delay labor for up to 48 hours. 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 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. 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. Atosiban was the most commonly used drug (42 percent), followed by nifedipine (34 percent), beta agonists (14 percent), and indometacin (8 percent).

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 reactions. There were no reports of serious reactions when women received atosiban or indometacin.

Combined or single treatment with beta agonists should be discouraged, concluded the researchers. They also recommended further trials to test the safety and effectiveness of nifedipine and atosiban.

In an accompanying editorial, the researchers said their study is a reminder that the decision to use tocolysis shouldn't be taken lightly.

"After 30 years of research, we still do not know whether tocolysis benefits the fetus, so the choice of which drug to use remains a secondary question. The real dilemma is whether or not we should treat at all," they wrote. The long-held belief that "keeping the baby inside longer must be a good thing" needs to be reevaluated, they said.

The study was published March 6 online in the BMJ.