An extra fertility treatment previously touted to save women the misery of miscarriages actually has no benefit at all, researchers say.
Endometrial scratching, or "womb scratching" is among a mix of add-on procedures that clinics have offered as part of in vitro fertilisation (IVF) services.
It involved sampling the tissue lining the womb, an action which was thought to result in a "scratch" or "injury" to the lining of the womb, and make it more receptive to an embryo implanting.
Costing as much as $295 in New Zealand, the process took about a minute and was similar to a smear test, but was more painful and invasive.
Now a large team of international researchers led by the University of Auckland's Professor Cindy Farquhar say clinics should stop offering it.
A 2016 survey of clinics in Australia, New Zealand and UK found that 83 per cent of doctors recommend endometrial scratching prior to IVF, especially to women with recurrent implantation failure.
"We knew that most clinics were offering this to their patients and we wanted to find out if it really helped women to conceive from IVF," said Dr Sarah Lensen, of the University of Auckland's Faculty of Medical and Health Sciences.
The team carried out a clinical trial spanning five countries, in which 1365 women from New Zealand, Australia, UK, Sweden and Belgium were randomly allocated to either receive or not receive an endometrial scratch before their IVF cycle.
The findings, published today in the New England Journal of Medicine, revealed no benefit from endometrial scratching.
The live birth rate was exactly the same among women who did and didn't have it (26.1 percent); nor was there any subgroup of women who appeared to benefit, including women with previous IVF failure.
No difference emerged in the rates of various other outcomes, including ectopic and multiple pregnancies.
Researchers also found that the procedure caused mild pain (self-rated 3.5/10 on average) and in some cases caused adverse reactions such as excessive pain or fainting.
"It is now clear that endometrial scratching does not increase the rate of live births," said Farquhar, who is also medical director of Fertility Plus at Auckland District Health Board.
"On this basis of this study, which is the biggest and most robust to date, we would encourage IVF clinics to stop offering it."
Infertility affects about one in seven couples.
Globally, women undergo over 1 million IVF cycles each year, but the success rate remains modest, at around 25 to 30 percent probability of a live birth per cycle.