Just so we're clear, brain activity was measured. Brain waves were not. You can't even measure a fetus's brain with an EEG until 20 to 24 weeks, simply because it does not have the required materials to think with until then. So I would recommend if you are going to abort, the first trimester or early second trimester is fine. Any later and you risk killing a conscious being.
But this is all retarded since fetal stem cell harvesting does not harvest from months old fetuses.