The only way you can believe that is to do two things: A) Ignore the dictionary meaning of the word "posterity," and B) Agree with Justice Blackmun that the fetus is not a person. Why? Because the Constitution explicitly protects the life of EVERY innocent person.
Even Blackmun, in the Roe vs. Wade written opinion, admitted that if the fetus is a person, they are "of course" protected by the Fourteenth Amendment.
And so, he dehumanized the child, with the result being the brutal deaths of more than fifty million defenseless, innocent persons.
One other thing: Even if one accepted the false notion that the unborn aren't "in the Constitution," the portion of your post that I quoted at the top of this reply has you doing exactly what the Ninth Amendment expressly forbids.
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
Funny thing...
The first reference from a Google Define: for "posterity" is a paraphrase of the preamble to the Constitution:
descendants: all of the offspring of a given progenitor; "we must secure the benefits of freedom for ourselves and our posterity"
-PJ