A study being conducted in the Netherlands has been halted after nearly a dozen babies succumbed to a serious lung ailment. Dutch doctors were trying to answer whether the active ingredient in the erectile dysfunction drug Viagra could be used to help a particular group of at-risk babies. The study was being headed by Amsterdam Universitair Medische Centra (University Medical Center), and followed the testing protocols of studies that had already been conducted in New Zealand and Australia.

The Dutch study, started in 2015, was designed to look at possible beneficial effects of increased blood flow to the placenta. The study followed 183 pregnant women who suffered from fetal growth restriction. Women who suffer from the condition have an underdeveloped placenta that is unable to provide enough oxygen or nutrients to a gestating baby.

More than a dozen factors have been attributed to the development of intrauterine growth restriction, including diabetes, high blood pressure, and several types of infection. Affected babies are often low-weight when born, can be stillborn, or may have long-term growth problems that last well into childhood. Low-birth-weight cases comprise about 20 million children born each year.

For the latest study, sildenafil, a generic version of Viagra, was given to 93 pregnant women to see if the drug would effectively increase blood flow to the placenta, which would then provide more nutrients to the babies. The 90 women in the control group were given an inert placebo. At the time they were treated, the mothers did not know which treatment they were receiving, which is standard in clinical trials.

Doctors across 11 hospitals participating in the study planned to study the mothers and their children through 2020. However, 19 of the babies born to the women treated with sildenafil died soon after birth. Eleven of those babies died from a form of high blood pressure in the lungs. Six more babies suffered the complication but survived.

Among the control group, just three babies had lung problems and none died. Around 15 women who took the medication have not yet given birth. Amsterdam UMC said in a release. “Based on these findings, the study stopped immediately.” There were no similar problems found for the babies in the previous studies. According to the release, the development of the children in the halted study will continue to be monitored and the data further analyzed.

In a statement, Pfizer, the maker of Viagra, said the company had nothing to do with the trial. The statement read, “Pfizer was not involved in any aspect of this trial, and neither funded nor provided product for the trial. In addition, the Principle Investigators at the Amsterdam University Medical Centre have confirmed a non-Pfizer manufactured generic version of sildenafil was used but that no clinical trial participants were administered Viagra, Pfizer sildenafil or any other Pfizer medicine.”