[Dr. Octagon]

Because conception, the forming of unique human DNA, happens before it. That's what renders it ambiguous. My DNA, the unique package that determines every physical trait I have, came into existence at conception. Not before, not after. Anything else is a viability test, and there begins the slippery slope.

[supercat]

Because conception, the forming of unique human DNA, happens before it. That's what renders it ambiguous.

In this context, for something to be ambiguous means that it's difficult or impossible to tell if it's happened. Implantation is not ambiguous; either it has happened or it hasn't.