No benefit from nifedipine widely used to prevent premature births

Nov 26 2008

New research from the U.S. has found that a drug widely used to prevent premature births offers no benefit.

Pregnant woman who enter into early labour are often given drugs to quieten the woman's uterus and prevent premature birth.

Pregnancy normally lasts 40 weeks and preterm births are defined as deliveries before 37 weeks of pregnancy - they have been on the rise in the United States and other developed countries and some research has found the increase in preterm births may be affected by factors such as smoking, lack of insurance and early intervention by doctors.

A trial where a popular drug was compared with a placebo found it worked no better at maintaining pregnancy after the initial bout of preterm labour is halted.

The scientists at the Stanford University School of Medicine, Lucile Packard Children's Hospital and Santa Clara Valley Medical Centre conducted the first trial which compared nifedipine to a placebo - nifedipine is a muscle relaxant originally developed to lower blood pressure.

Dr. Deirdre Lyell, an assistant professor of obstetrics and gynaecology at Stanford and the study's lead author, says the use of medication should be minimized in pregnancy unless it is clearly indicated and even though the serious side effects of nifedipine in pregnancy are rare, even a low risk is not worthwhile if the drug has no benefit.

Dr. Lyell says preventing preterm birth is important, but prolonged treatment with nifedipine does not appear to be an answer.

Dr Lyell says preterm babies face health problems such as respiratory distress, bleeding on the brain and tissue-destroying intestinal infections - long-term complications include neurological disorders, chronic lung disease and vision and hearing problems and the earlier the delivery, the greater the risks and this means doctors are highly motivated to help women in early labour stay pregnant as long as possible.

For the study Lyell's team recruited 71 women who had been successfully treated for preterm 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 nifedipine would prevent preterm labour from re-starting and evaluated whether subjects' pregnancies lasted to 37 weeks and measured how long delivery was delayed and also noted the babies' gestational age at delivery, birth weight and complications of prematurity.

The team found no differences between nifedipine and placebo for any measurement - about 40% of the women in both groups reached 37 weeks of pregnancy, with delivery delayed an average of a month and the babies' average health was the same in both groups.

The study was designed to detect a 50% improvement in delayed deliveries and Dr. Lyell says if nifedipine confers a smaller advantage, it would not have been spotted in this study, and she suggests a larger study of nifedipine is warranted.

Based on the current lack of data to support this drug, Dr. Lyell believes obstetricians should proceed with caution as all medications have side effects and nifedipine despite a fairly good safety record, in a few cases it has been linked it to dangerously low blood pressure in pregnant women.

Dr. Lyell says every now and then, there will be a patient who has an unusual side effect and it is important to distinguish between acute treatment, which is given to a woman in preterm labour, and maintenance treatment, which is given to a woman following an episode of preterm labour that has ended - she says this study addresses maintenance treatment.

The study was funded by research funds from the Departments of Obstetrics and Gynaecology at Stanford University and at Santa Clara Valley Medical Centre, and is published in the December issue of the journal Obstetrics and Gynaecology.