What’s the source of this definition of baby? And whose determination is it that brain waves and/or some arbitrary level of sentience is the key defining factor?
“While we have no good standard for measuring consciousness or determining when a morally meaningful level of consciousness has been attained, we can safely say that a six-week-old fetus is in no sense sentient, despite exhibiting brainwaves. While brainwaves are a necessary precursor for sentience, so are neurons, which start developing much earlier. In short, the initiation of brainwaves does not mark a transition in sentience at all, and there is no reason to claim that initiation of brainwaves marks a transition in cognition or even the ability for future consciousness that is any more significant than a multitude of other developmental landmarks. As a result, it is an arbitrary and inadequate threshold.” (Source)