Maternity benefit won't back pay!

Maternity benefit needs to be activated. We only realized that this benefit needs to be activated at 38 weeks pregnant only to find out that discovery won't pay back the Gynecologist and blood test we already paid from our savings account. Why does this benefit need to be activated and even if there is a good reason why can't you back pay if you register later. We did a pre-authorization at the hospital in the beginning of the pregnancy. Very frustrating!