I am a father of 4 and soon to be 5. I want a vasectomy but my wife is refusing.

All of our kids are boys and my wife is 38. She wants a girl which is why we are having a 5th. She wants to keep trying till she gets a girl. She has agreed to stop if our 5th is a girl but otherwise she refused to stop. She refused to let me get a vasectomy even though we are financially burdened by our 4 kids.