Is this a normal doctors office thing?

October Momma • 22 year old happily married mother of boy girl twins, Emma and Alden, born 10/11/17😊
I got a letter today saying I owe $444 for the delivery of my baby due the 28th week of pregnancy. I have to pay half of that amount by the 20th week to receive a 20 week ultrasound or they will withhold the ultrasound until I pay it. Is is normal for doctors offices to charge you for the birth of your child before the child is even born? I'm only 14 weeks pregnant and that means I only have 6 weeks to cough up $222 that I was not told about a month ago when I was there. I know that isn't a lot, but why should I pay for the birth if the birth hasn't taken place yet?