About five percent to 10 percent of pregnant women go two weeks or more past their due date, a delay that raises the risk of complications during labour. Because of this, doctors routinely induce labour when a pregnancy lasts beyond 41 weeks.

During standard labour induction, the doctor uses an instrument to rupture the amniotic sac or gives synthetic forms of prostaglandins or oxytocin - hormones that normally help trigger labour.

Acupuncture has been promoted as an alternative; in theory, it may work by stimulating the nervous system, which in turn could cause the uterus to contract.

But in the new study of 364 pregnant women who were past their due dates, Australian researchers found that two days of acupuncture therapy did not reduce the need for standard forms of labour induction.

Dr. Caroline A. Smith and colleagues at the University of Adelaide report the findings in the journal Obstetrics & Gynaecology.

Acupuncture has been used for more than 2 000 years in Chinese medicine to treat a wide variety of ailments. According to traditional medicine, specific acupuncture points on the skin are connected to internal pathways that conduct energy, or qi ("chee"), and stimulating these points with a fine needle promotes the healthy flow of qi.

For their study, Smith and her colleagues randomly assigned patients to either undergo real acupuncture or a "sham" version where needles were inserted only superficially, into areas of the skin other than traditional acupuncture points.

Each woman had two sessions performed over the two days before her scheduled labour induction.

In the end, Smith's team found, women who had the real acupuncture were just as likely as the comparison group to need any of the standard forms of labour induction and did not have a shorter labour once it was induced.

Still, the researchers conclude, the findings do not prove that acupuncture has no use in inducing labour. They say larger studies should look at whether starting acupuncture sooner, or doing more sessions, aids labour induction.

In the meantime, acupuncture at least seems to do no harm.

"There is no evidence of harm from the administration of acupuncture in the postterm period to the mother or foetus," Smith and her colleagues write, "and women may still seek out the use of acupuncture to prepare for labour."