The question really boils down to this. Is it okay to save babies from abortion and not tell the mother & father about Jesus? Well, I think the answer is a little yes and no.
Saving the life of a child is always the right thing to do. Saving a mother and father from the life altering and irreversible decision of having an abortion is also the right thing to do. Here's an example. You are walking down the street and you see a guy engrossed in his phone as he's texting someone. You notice that he continues walking with his head down as he nears the corner and is about to step out into traffic unaware. You yell at the last second "watch out!" The man immediately stops and looks up from his phone, now realizing that he was one more step away from being seriously injured or killed by oncoming traffic. He looks back at you with wide eyes and says "thank you!"
Obviously it is always morally and spiritually right to do what you can to save this man's life. Yet does the yelling of "watch out" do anything to lead this man closer to a personal saving relationship with Jesus? Possibly? Because you yelled his life was saved and both he and his family are grateful. However this man will still at some point die and face eternal judgment.
Back to the mother & father in crisis. In the same way we want to do everything in our power to persuade them to not abort their child. This is always morally and spiritually right. However if this is our only goal in pro-life ministry we have made a huge mistake. In one way you have helped them greatly and that should not be underestimated. At the same time the judgment is still coming for them and if they do not know Jesus then they are guaranteed eternal separation and judgment.
We are the ones with the good news! Not only do we know the good news, better still he lives inside us. If we do not tell them then who will? And if they are not ready to hear the gospel in one of their greatest trials of life then when will they be ready? As people who know Jesus personally we must continue to do everything we can to save the lives of all involved mother, father, and child. In doing so let us not keep the "good news" to ourselves.