The DOI is the founding document, principled in natural rights that apply regardless of any and all other statements.
The Declaration states the decision of the Colonies to separate from the Crown, and their reasons for doing so. It doesn’t make Law.
If you want the unborn to be considered full-fledged citizens with all rights to due process, you will need to have that codified into law. Just because we believe something is ‘right’ doesn’t make it the law of the land.