Amsterdam University Medical Centre (AUMC) has recently stopped a trial designed to test whether the drug sildenafil, a medicine commonly used to treat erectile dysfunction, could encourage growth in unborn babies.

The study, which involved giving the drug to pregnant women whose babies had severe growth limitations caused by an underdeveloped placenta, was being carried out across eleven hospitals in the Netherlands and was due to run for five years, ending in 2020.

The “Sildenafil therapy in dismal prognosis early onset fetal growth restriction”, or STRIDER, trials were designed through international collaboration and due to take place in New Zealand and Australia, Canada, Ireland, the Netherlands and the UK.

Babies with an undeveloped placenta are at risk of being born prematurely, have very low birth weight and poor chances of survival. Currently there is no effective treatment for foetal growth restriction. To date the only form of assistance is intensive foetal surveillance with elective delivery (when foetal acidosis or foetal distress is evident).

Sildenafil dilates the blood vessels and is most commonly used for erectile dysfunction in men but is also prescribed for people with pulmonary hypertension (high blood pressure within the lungs). The aim of the study was to see if the drug could encourage a better flow of blood through the placenta, promoting the growth of the child. This seemed to have been supported by recent experimental animal and in-vitro research.

Interim analysis by AUMC showed that Sildenafil may be detrimental to the baby after birth with the hospital stating “The chance of a disease of the blood vessels of the lungs appears to be greater and the chance of death after birth seems to have increased”. The researchers found no positive effect for the children on other outcomes and adverse effects occurred after birth. The drug did not have an adverse effect on the mothers.

At the time of termination over 183 women were involved in the study, of which 93 women had taken the drug while the remaining 90 were given a placebo. Twenty babies developed lung problems after birth – three in the placebo group and the remainder in the treatment group. Of the Sildenafil group, eleven babies died due to these lung complications. In the placebo group nine babies also sadly died but not of lung disease.

The results from this Dutch study are all the more surprising because the complications do not appear to have been seen in two other, similar trials that have already taken place in the UK and Australia and New Zealand.

The UK trial took place between November 2014 and July 2016 and 19 medical units in the UK participated. 135 women were recruited, 70 of which received the drug Sildenafil and 65 received a placebo. Within this group livebirths, foetal deaths, neonatal deaths and birthweight did not differ between groups. In addition, of the eight serious adverse events which were reported during this trial - six of them were in the placebo group and none of these were attributed to Sildenafil.

A full investigation into why so many babies sadly passed away in the Netherlands is underway. Similar research being conducted in Canada has also been temporarily suspended. Whilst it is clear that research into this area is extremely important, taking into account the high risk of neonatal death, it unfortunately seems that, Sildenafil cannot offer the breakthrough many might have hoped for in babies with underdeveloped placentas.