A world-first clinical trial is about to get underway in New Zealand and Australia to see if the drug Viagra can also improve the survival and health of unborn babies.

Sildenafil, the drug commonly known as Viagra, can improve male sexual function by increasing blood flow to the pelvis.

Researchers from Gravida - New Zealand's government-funded National Centre for Growth and Development - believe the drug may hold the key to improving the survival and health of babies who stop growing in the womb.

Dr Katie Groom, who is leading the clinical trials for Gravida, says there is currently no treatment to help mothers who experience this.

"If we have babies that end up needing to be delivered before 28-30 weeks because they're so small, then probably overall the risk of still birth or long-term handicap might be as high as 70-75 per cent," she said.

"These babies would really benefit from better growth and being able to stay in the womb for longer.

"One of the things I find most challenging in my job [is] when you have to make a diagnosis and then say, 'I'm sorry, there's nothing we can do.'

"All we can do is watch mum and baby very closely. [We're] basically watching the babies until we think that they're the size and age where we think there’s a chance of survival if we delivered them.

"Then we have to ... [balance] the risks of leaving the baby inside - and therefore the risk of a still birth - or the risk of delivering them. That's really the only option we can offer."

Animal trials showing promising results

Dr Groom says the trials will investigate whether the drug can increase foetal growth by increasing nutrient supply across the placenta.

"Obviously, [the drug is] famous for increasing the blood supply to the male pelvis but what we're looking at is the potential to increase blood supply to the female pelvis, and therefore increase blood supply to the placenta," she said.

"The work that's been done up until now has been looking at samples of muscle from the uterus and from the placenta from women who've had these conditions and applying sildenafil or other types of drugs and making comparisons that show improvements in the blood vessels.

"In some studies within small animals - looking at babies that are growing - [we've seen] sildenafil ... showing that it does improve growth.

"We've now got the opportunity and we think we've got enough evidence to show proof of principle that we should start to have a look and see whether we can help women whose babies are really small."

Trials to start later this year

Clinical trials are due to start in New Zealand and Australia later this year.

The trial will monitor 122 pregnant women carrying extremely low-growth babies who will be given Sildenafil or a placebo during their pregnancy. 

International trials will follow before any conclusions are drawn, but Dr Groom is hopeful the drug will save lives by allowing at-risk babies to be delivered closer to term, and healthier.

"It's got really exciting potential but I think it is important to stress at the moment it is potential," she said.

"We certainly don't recommend that anybody should be taking this drug outside of a clinical trial and very close supervision.

"We are still a few years away from getting an answer, but if this does improve babies' growth it would be a real breakthrough in terms of our management of fetal growth restriction."