16 February 2015. How much evidence do we need before we can decide? It may be a surprise, but the U.S. Food and Drug Administration (FDA) is showing the way. The FDA had become aware that many parents like to get an ultrasound picture of the baby while still in the mother’s womb. It has even become fashionable to record a video of the fetus’ movements. But the FDA warns that it is a bad idea. Not that there is evidence that this practice is dangerous to the fetus, especially the brain. In fact there is no such evidence. Nonetheless, FDA voices precaution, as adverse effects are possible and cannot be excluded. Given the lack of health benefits or other advantage of ultrasound videos, this practice should stop, the FDA says. The Lancet has praised FDA’s initiative, and we do too. Let this be an example of how to deal with plausible, yet unproven risks to brain development.