With DS I had to pay a copay every time. I had an HMO. It really added up at then end when I was going every other day. Check with your insurance because sometimes you pay 1 copay for all prenatal care and sometimes you have to pay at each appointment. It just depends.
This time around I have a PPO w/ coinsurance. So my Dr has all ready figured out what I will owe them and given me a discount rate as long as it is paid before the baby is born.
FYI - If you have a PPO talk to your Drs billing office about this. My bill would have been $4500 but they have discounted it to $2500. I'll still have my hospital coinsurance to deal with after the baby is born but taking 2k off the top is going to help a lot.