Dutch researchers have stopped a clinical trial involving pregnant mothers treated with Viagra after the death of 11 newborn babies.

The women taking part in the study were given the anti-impotence drug Sildenafil, sold commercially as Viagra, to improve the growth of unborn children with poorly developed placentas.

It is thought the drug, which promotes blood flow, might have caused lethal damage to the babies’ lungs.

The ABC has reported that a Queensland study using Sildenafil has also been halted.

The Dutch study is part of broader research conducted in Australia, New Zealand and the UK looking at the use of Sildenafil early in pregnancy.

The ABC says the Queensland trial is significantly different to the Dutch one and quotes Sailesh Kumar, from the University of Queensland and the Mater Research Institute, who said his study aimed at reducing foetal distress during childbirth and used a much lower dose of Sildenafil and for a much shorter period.

“It’s a very, very different study [from the Dutch trial] and the drug is used in a very different context,” Professor Kumar said.

“The women in our trial used up to three tablets — but generally only one tablet during labour.

“I spoke to the lead investigator of the Dutch study where there was an unexpected spike in the number of neonatal deaths in the group of mothers who received Sildenafil.

“And because of this, [the child deaths] … and also because the overall result did not show any benefit in terms of improving growth of these babies, they stopped the study.”

When the Dutch trial was stopped, roughly half of 183 pregnant women involved in the study were taking Sildenafil, participating hospital Amsterdam University’s Academic Medical Centre said.

The study started in 2015 and involved 11 hospitals. It was designed to look at possible beneficial effects of increased blood flow to the placenta in mothers.

About 15 women who took the medication are yet to give birth.

“Previous studies have shown that Sildenafil would have a positive effect on the growth of babies,” the AMC said. “The first results of the current study showed that there may be adverse effects for the baby after birth.”

The results showed 17 babies were born with lung conditions and 11 died. Among the roughly equal control group, just three babies had lung problems and none died.

“The researchers found no positive effect for the children on other outcomes,” the AMC said.

Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, told Reuters the small number of trials with pregnant women meant there was limited knowledge of the effect of medicines in pregnant women.

“There have been other studies in this area, both involving preliminary work using animals and using pregnant women, and there was no indication that the treatment was dangerous based on previous research,” he said.

Viagra was originally developed by Pfizer but is now off-patent and available as a generic.

-with AAP