I don't understand what benefit they think this could have. At best, it's just going to delay amicable spanorces by a few months, since it doesn't stop postpartum spanorces. In practice, a couple that wants to separate can still do so regardless of pregnancy, just waiting until the kid is born to sign the papers and make it official. It's going to do nothing to stop kids from having spanorced parents, which is about the only potential benefit I could believe they're fishing for (though even then, being raised by parents that should spanorce but don't/can't is generally worse for kids than being raised by parents that spanorced when they should have).

The only time it'll actually have an impact is when only one party wants out (abusive situations being the most obvious example), and then the impact is overwhelmingly negative because it means that person is trapped in a relationship they don't want (which may even be outright dangerous). Nothing about this makes sense.