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.