OP is relying on a strawman themselves by continuing to use the term “pro-life” to represent the anti-abortion side of the argument. One can be in support of legal, safe access to abortion and still feel that abortion is against their own moral values.
A true “pro-life” stance should by its very definition include the lives of those who could potentially be harmed by carrying a high risk or unwanted pregnancy to term, as well as those of the children born into situations in which their basic needs are unlikely to be met. And yet, far too often we see those who label themselves “pro-life” completely ignore the value of these lives.
The phrasing you reference is not intended to reference a theistic creator, rather as a way to acknowledge that it is not the role of government to confer rights to the people - we are owed them inherently. “Our creator” could just as readily be interpreted to mean a series of entirely natural processes that can be explained by scientific principles.
The founding fathers themselves explicitly acknowledged that the government was not founded on religious principles on many, many occasions. If you need more details on this, the anti-defamation league has compiled several good quotes here: https://www.adl.org/sites/default/files/documents/assets/pdf/civil-rights/religiousfreedom/PORF-StatsFF.pdf
You are free to believe (or not) in anything you like, but there is no place within our government for the consideration of religious beliefs in how we make or apply our laws.