A major New Zealand Australia clinical trial has found some evidence that mothers taking Viagra during pregnancy could help babies suffering from stunted growth in the womb.

Viagra is used to treat male erectile dysfunction by dilating blood vessels in the pelvis. The researchers wondered whether it might work the same way in women by increasing blood supply to the placenta.

Fetal growth restriction, also called intrauterine growth restriction, is when a baby cannot grow properly due to problems with the placenta.

It affects 5-10 per cent of babies, or between 3,000-6,000 each year in New Zealand. In the worst cases stunted growth can lead to stillbirth or to babies being born very small and at high risk of disabilities, developmental problems, short-term and later illness.

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There is no treatment except early delivery, which can make long-term problems worse.

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The study, led by the University of Auckland and overseas colleagues, involved 122 pregnant women from New Zealand and Australia. Half regularly took sildenafil - brand name Viagra - and half took a placebo.

The researchers found no effect on in-utero growth, but did detect a trend towards higher survival of the babies in the sildenafil group before and after birth: 81 percent, or 51 out of 63 babies compared to 73 percent, or 43 out of 59 babies, in the control group.

They also found that 11 percent more babies in the sildenafil group survived free of major illness before leaving hospital, and their mothers had fewer new cases of pre-eclampsia, a serious pregnancy complication (14 per cent versus 23 per cent).

Lead researcher and associate professor Dr Katie Groom said the study was so small that the difference may not be statistically significant.

This would be a very important difference, really having the potential to change lives in the future

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"However, if we saw the same differences in a larger group of mother and babies, this would be a very important difference, really having the potential to change lives in the future," Groom said.

The study is part of a wider network of four trials across five countries. A UK trial looked at the effects of Viagra on severely growth-restricted babies, and found it did not prolong pregnancy, improve survival or reduce short-term illness in the babies after birth.

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"Babies in the UK trial were sicker and needed earlier delivery than the babies in our trial, so it is possible with more time available for the drug to make a difference that we may find a different result to this British study," said Groom, who is also a Hugo Charitable Trust Research Fellow and obstetrician at Auckland City Hospital.

Results from the other two trials – across Canada and The Netherlands – are expected by the end of 2020.

"Combining all four trial results should tell us with certainty whether our finding was real or chance, and whether or not to pursue sildenafil as a therapy for the future."

Researchers are now assessing the development of the surviving babies from the Australasian and UK trials at ages 2-3.

Groom will present the study's findings at a conference on mother and baby health research this morning. She will also speak at tomorrow night's Liggins Institute Public Lecture, "A Healthy Start to a Healthy Life", at the University of Auckland Fale Pasifika.

Archie McDonnell, aged 3 and a half, is doing just fine despite being growth-restricted in the womb and born premature at 30 weeks. Photo / Supplied
Archie McDonnell, aged 3 and a half, is doing just fine despite being growth-restricted in the womb and born premature at 30 weeks. Photo / Supplied

Archie's story: 'We dodged every medical bullet'

Archie McDonnell, three-and-a-half, seems fine now. But at birth he weighed just 795g, thanks to problems with his placenta which had stunted his growth in the womb.

His mum Anne was referred to specialist care at 24 weeks, and met Dr Katie Groom, who was leading the trial of Viagra for growth-restricted babies.

She and husband Deane talked it over and agreed to participate.

"This could potentially really help the child if I was on the drug, and if I was on the placebo instead, I'd still be getting amazing monitoring and the best care, so it was a win-win situation," Anne said.

Archie's condition deteriorated and Anne was admitted to hospital at 27 weeks, where she developed pre-eclampsia. Archie was born by caesarean section at 30 weeks.

"He was tiny, so small. He was fragile, his skin was translucent, he just looked so vulnerable. We couldn't hold him, we couldn't feed him, we couldn't dress him," Anne said.

Archie started life in an incubator, on constant oxygen support, and was fed intravenously for seven weeks.

"I remember at two and a half months when he was taken off all the monitors, I walked to the window with him in my arms and I burst into tears because it was the first time I was able to walk anywhere with him."

After three months – 91 days - Archie was discharged from Auckland Hospital. Archie continues to contribute to science through participating in the follow-up study that assesses the children's development at two to three years.

"He's a bit smaller than his peers, but there are no developmental effects," Anne said. "We know how incredibly lucky we are – we talk about the fact we dodged every medical bullet we possibly could have."