In the first place, most abortions happen well after the unborn child is that small, and only a moron could see a sonogram image of an unborn child and dismiss it as mere tissue. 

Beyond that, if size is the yardstick for constitutional rights, how big does a human being have to get before it starts having these rights?  Is weight or height the determining factor?  Do these rights come on gradually as size increases and, if so, what is the ratio of size to rights?  Should men have more rights than women since they are generally larger?  If someone loses weight do they lose rights?