A Kiwi trial is exploring how giving pregnant women the drug Viagra may help underweight babies before and after birth.

Being born too small poses major, life-long risks of handicap and disease, yet there remain no treatments available to improve growth before birth, leaving early delivery as the only option.

A trial led by researchers from the University of Auckland and overseas colleagues used a curious agent - erectile dysfunction drug Sildenafil, sold under the brand name Viagra, among others - for what could be the first ever in-utero therapy for fetal growth restriction.

Under the STRIDER NZAus study, the drug was being given to mothers with pregnancies affected by severe fetal growth restriction across New Zealand and Australia and compared to a similar group of mothers who receive a placebo tablet.

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"The theory is that Viagra increases blood supply to the male pelvis and therefore it's selective to those pelvic vessels," said Dr Katie Groom, of the university's Faculty of Medical and Health Sciences.

Groom and her colleagues want to know if the drug could increase blood supply to the placenta, which, if short of blood, could result in growth restrictions for babies and women developing the pregnancy complication preeclampsia.

There had been promising indications from early studies, including one that analysed blood vessels from women who had undergone cesarean sections, and another using animal models.

"There was another very small case control series done in Canada about 10 years ago, and it looked like the drug helped their babies to grow, so we came up with this idea of taking it to a proper, randomised control trial."

An international effort split into five trials was launched, with 122 women recruited for the New Zealand and Australian study.

"That doesn't sound like a lot, but because of the degree of the severity of the condition, we worked out that would be enough to get an initial message of whether or not the drug has had a positive effect."

The study had now reached the point where the majority of babies had been delivered, although not all had survived.

"We monitored the pregnancies really closely, and we've monitored the babies really closely once they were born and went through the neo-natal unit.

"Whether or not we find a difference in how the babies grow, what's really important is how they do once they start to grow up."

The next part of the research, called the STRIDER NZAus Childhood Outcome Study, will assess the development of the surviving babies at the ages of two and three.

Jointly funded by the Auckland Medical Research Foundation (AMRF) and the Neurological Foundation, Groom and her colleagues will assess whether using Viagra in pregnancy improved neurological, emotional and behavioural development, as well as their cardio-metabolic, respiratory and general health.

"Hopefully by the end of this year, we'll have the results of the first phase of the trial, which looked at how they did until they left hospital, and then we'll have the opportunity to follow them up when they're older.

"Even if we find the drug has made any difference, this follow-up study is really valuable because this is a unique cohort of babies and, until now, we really haven't known how well these babies do."

Having the data would also give clinicians clearer information if the treatment was recommended to mothers in the future.

A separate experimental study, also just funded by the AMRF, is using sheep to find whether the treatment could reverse the increased risk of metabolic disease after pregnancies with growth restriction problems, by looking at markers of glucose metabolism in the fetal pancreas, liver, and muscle.

Other AMRF studies, which have received more than $1.2 million in the latest round, will research new strategies to avoid fatal stent failure during heart surgery, how preterm infants could be protected from brain injury, and a potential new biomarker for cognitive impairments associated with Parkinson's disease.

"We believe that research is the backbone to creating advances in medicine," AMRF executive director Kim McWilliams said, "and we are proud to continue to support these advances by funding exceptionally high quality research in our latest grant rounds".