Birth determines, not personality, but civil personality only. For personality does not begin at birth, it begins at conception. An unborn child from its conception has personality. No less than the Constitution recognizes the life of the unborn from conception. Likewise, the Supreme Court held in Continental Steel Manufacturing Corp. vs. Montano that a child inside the womb already has life.
Life, however, is not synonymous with civil personality. Hence, a foetus which may have acquired personality at conception must be born later for it to possessed legal personality. Hence, Article 40 merely provides that a conceived child acquires civil/legal personality when it is born, and Article 41 defines when a child is considered born.