Once the baby is born, you could get an IUD or go on the pill, it is not necessary to tie your tubes at the time of the birth. That would give you more time to think about whether you want a permanent method of birth control or not.
Incidentally, you should speak to a lawyer about the baby. By law, since you are still married, the baby is considered to be your husband's. If you do not want this for whatever reason (and probably just to have a correct record of the baby's paternity) you might need to take some steps with the birth certificate or do something else. The baby's father -- is he going to be in the baby's life? You'll need an attorney's help for child support issues, too.
I have seen many women here tie their tubes and regret it later on. I agree with Mum2beagain..if you are going to do it, make absolute certain it is what you want. It is reversible (sometimes), but only at great expense.
Tying your tubes is a permanent method of birth control. Do it if you are certain you will not want anymore children.