Ex gf 30 weeks pregnant and needs extra scans she says its bcause pregnancy is high risk. She wants me to cough up 50% payment for them. She's paid for the other ones so why not pay for these herself too?

If that's your child, I believe you had just as much fun making him/her as she did. You are just as responsible for the cost and rearing of the child as she is. If you didn't want that responsibility....well, it's too late for that....you HAVE that responsibility and that child depends on you and her for care. Time to grow up, be a big boy, and face your responsibility like a man.