A new study, released Wednesday in the Journal of Physiology, has shown that giving Viagra (sildenafil) to pregnant women could increase the risk of fetal growth restriction.
The study, conducted on sheep, found that the drug impaired the ability of the fetus to redirect blood supply to essential organs, supplying low oxygen and causing fetal growth restriction due to poor placental blood flow.
The study finding was especially important because researchers were about to conduct a large human study investigating maternal Viagra in pregnancies affected by fetal growth restriction as a potential therapy for improving fetal growth and correcting impaired placental function by boosting blood flow.
This human study was halted early after the researcher found that maternal Viagra treatment resulted in increased fetal death rates. However, the exact mechanism behind the increased death rates was not clearly understood.
The authors said, “Our study provides crucial insight into a potential mechanism underlying the increased morbidity.”
“We show that prenatal sildenafil lowered levels of oxygen in the fetal blood, but despite this, the fetus did not respond by redirecting blood to essential organs. This finding may underlie the adverse outcomes observed clinically,” they added.
Viagra, which is often prescribed to men with Erectile Dysfunction (ED), dilates blood vessels and increases blood flow to certain parts of the body, which is why scientists were investigating the drug’s ability to potentially improve fetal growth by increasing placental blood flow.
However, the researchers found that Viagra can cross the placenta and cause certain effects on the fetus. The findings highlighted the importance of pre-clinical studies in animals before conducting large human trials.
“Our study replicated the impaired placental function that was observed clinically, in fetal sheep as a pre-clinical model. Using sheep as a model organism, we were able to implant monitoring equipment into these fetal sheep to monitor changes in both maternal and fetal blood flow and physiology in response to low oxygen levels in the blood and Viagra treatment,” the researcher explained.
They noted that a key difference between their study and the previously discussed clinical trials is the way they delivered Viagra.
Previous clinical studies involved oral administration of Viagra to the mother, whereas the current study researchers administered the drug intravenously. This could result in different circulating levels of sildenafil in the blood.
The researchers could not investigate the effects of Viagra on a healthy fetus, although their findings demonstrate the effects of the drug in a growth-restricted fetus. The study’s first author Ishmael Inocencio said, “A key finding of our study was the unexpected exacerbation of growth restriction following Viagra treatment. This has important implications for the danger of administering this drug to pregnant women.”
