I'm sorry, this is not anywhere close to "settled science." As just one example, you have molar pregnancies, ones in which, while there is "conception" and even "implantation," only a mass of tissue grows and not a fetus/baby -- though the tissue is arguably "human tissue."
Another scientific claim is based on what it means to be "human." Is a dead person a "human," in the same terms as a fetus is? Or is death when we stop being "human?" Scientifically, higher brain functions are typically what determines "life" -- yet a fetus doesn't have higher brain functions until at least week 23 (which is roughly the soonest they can survive outside the womb). By this argument, then science would say that "humanity" really begins around 23 weeks.
While many scientists agree with the "23 weeks" claim, it is not "settled science," but the scientific claims for "human" would appear to be closer to 23 weeks than conception.