Medication use should be minimized in pregnancy unless it's clearly indicated, said Dr. Deirdre Lyell, assistant professor of obstetrics and gynecology at Stanford University School of Medicine, and the study's lead author.
Working in collaboration with researchers from Lucile Packard Children's Hospital and Santa Clara Valley Medical Center, Lyell recruited 71 women who had been successfully treated for pre-term labour between 24 and 34 weeks of pregnancy.
The women were then randomly assigned to receive doses of nifedipine or placebo every six hours until 37 weeks of pregnancy or until delivery, whichever came first. The researchers hoped that nifedipine would prevent pre-term labour from re-starting.
Lyell and her colleagues evaluated whether subjects' pregnancies lasted to 37 weeks and measured how long delivery was delayed. They also noted the babies' gestational age at delivery, birth weight, and complications of pre-maturity-such as neurological disorders, chronic lung disease, and vision and hearing problems.
She said that there were no differences between nifedipine and placebo for any measurement.
She revealed that about 40 percent of women in both groups reached 37 weeks of pregnancy, with delivery delayed an average of a month, and that babies' average health was the same in both groups.
Lyell cautioned that the study was designed to detect a 50 percent improvement in delayed deliveries, and that any smaller advantages of nifedipine use would not have been spotted.
She thinks a larger study of nifedipine is warranted.
A small benefit would be especially significant at early gestational ages, and less so later on. But overall, there's no benefit to pre-maturity, she said.
Since there is a lack of data to support nifedipine use, Lyell believes obstetricians should proceed with caution.
All medications have side effects, she said.
The drug might be having a fairly good safety record, but some case reports link it to dangerously low blood pressure in pregnant women.
If something has not been shown to be of benefit, it shouldn't be used. Every now and then, there will be a patient who has an unusual side effect,Lyell said.
It's important to distinguish between acute treatment, which is given to a woman in pre-term labour, and maintenance treatment, which is given to a woman following an episode of pre-term labour that has ended. This study addresses maintenance treatment. We still use nifedipine for acute treatment of pre-term labour, she added.
The findings of the study will appear in the December issue of the journal Obstetrics and Gynecology.