Earlier this week, Amsterdam University Medical Centre (UMC) announced an early end to a clinical trial testing a new use for the pharmaceutical sildenafil in the wake of newborn deaths.

The drug – known commercially as Viagra, although in this case the researchers used a generic version of it, not one produced by Pfizer – is popularly used to treat erectile dysfunction by improving blood flow.

Encouraged by preliminary tests, doctors had hoped to use those same vasodilating properties to stimulate the growth of placentas.

"We wanted to show that this was effective to promote growth among babies," lead researcher and gynaecologist Wessel Ganzevoort told the daily newspaper, de Volkskrant.

"But the opposite has happened. I am shocked. The last thing you want is to harm patients."

Sildenafil works by blocking an enzyme that breaks down a messenger compound that helps relax smooth muscles, such as those surrounding certain blood vessels.

The result is an increase in blood flow, which not only has a use in managing erectile function but in reducing the severity of mountain sickness symptoms and in treating pulmonary hypertension.

Now that it's no longer under patent, the drug is being explored by research companies as a wonder drug for a range of other conditions.

One application that initially showed promise was as a way to dilate blood vessels in placentas that were stubbornly slow to develop, a condition that increased the risk of babies being born prematurely and with low birth weights.

"The prognosis for such babies is poor and there is no known other treatment for the child," said the UMC statement.

Recent randomised clinical trials comparing the drug with a placebo had detected no adverse effects on healthy mothers or infants, giving the all clear for others to conduct further testing.

In fact, the buzz on its potential has been building over the years, with rumours that doctors have already been suggesting pregnant women take the drug.

"Foreign colleagues let slip that they sometimes prescribed it, with good results," says Ganzevoort, who was also careful to point out how doctors in the Netherlands are more cautious.

"I have experienced in my own consulting room that pregnant women asked for it."

Exactly what went wrong in this trial remains a mystery.

In 2015, hospitals in the Netherlands recruited 183 women whose pregnancies were likely to be adversely affected by placental development. Roughly half were prescribed a placebo.

An evaluation carried out by an independent board took a closer look at 19 deaths of newborns delivered to mothers who had received the medication during their pregnancy.

Crucially, 11 of those babies were diagnosed with elevated blood pressure in their lungs, presumed to be linked to the drug.

Six other newborns also had a lung condition depriving them of sufficient oxygen, but had survived.

To put those figures into context, nine infants in the placebo group also passed away soon after birth. None of them showed signs of that particular lung condition.

The study had been set to continue until 2020. In spite of the trial's cancellation, around a dozen women are still waiting to see how the drug could affect their pregnancy, and are being closely monitored.

It's not clear where the research will go from here. The results are shocking, but also completely unexpected.

"We need to be careful at this point to find out more," foetal medicine expert Zarcko Alfirevic from the University of Liverpool told the BBC.

"It needs a thorough investigation because the complications were not seen in the two other, similar trials that have already been done in the UK and Australia and New Zealand."

Sildenafil is obviously a drug with a great deal of potential. Giving placentas a boost could still yet be one of them.

But it's a tragic example of why even the most promising of treatments needs such extensive experimentation, no matter how much promise they show.