Hi Dhav,
Interesting question. Most reiki masters and practitioners will not give a pregnant woman a reiki session and certainly not attune her whilst in that condition. The babies do not generally inherit any 'attunement' or reiki ability, but I am seeing more and more children that already use reiki and do not need any attunement. Perhaps this is because of the opening up of the world due to the internet, perhaps it is that more people know what reiki is, perhaps they learn from their parents or families.
Of course your question revolves round the belief that to channel reiki one has to be attuned first....