HIE stands for hypoxic-ischaemic encephalopathy, and put simply, is a lack of oxygen to the brain before, during, or shortly after labour (it can happen in older children too). This can cause injury, and the severity of this can vary greatly (often given a grade from 1 which is mild to 3 which is severe). Tests are often done at an early stage to determine the extent of any damage, but one thing to remember though is that babies have a tendency to do their own thing, despite what any results may suggest!
There are many potential causes of HIE, such as placental abruption, umbilical cord-prolapse, uterine rupture and shoulder dystocia. There are lots of other possible causes (too many to list here) so best to seek a medical opinion if further details are needed.
From experience, HIE isn’t really that well known, but it affects 3-4 in every 1000 babies. Peeps is trying to raise awareness, so that others know more about it and that more people affected by it can get the support needed.