cervical biopsy

I am 16 weeks and 3 days and i am scheduled to have this procedure done the 14th of this month. Ive had one done before but not pregnant. The more i read into it..the more it scares me cause it stated it can cause a miscarriage.. i mean its my right to refuse this until the baby is born and get it done right? I wouldn't see why not. This is my 3rd pregnancy by the way and i had already had small amounts of blood forming between the placenta and uterus. Just need advice. The more i think about it the more uncomfortable i become with it