There are so many disturbing, judgmental posts in this thread. Bluelight is meant to be a place people come to get accurate harm reduction information. Do you really think someone who is pregnant would bother posting again, given the abuse from some of the posters and moderators here?
The most danger to the fetus is from withdrawal. Being stabilised on methadone or bupe is the safest option. Continuing to use means that you'll end up putting the baby under a lot of stress. Not all babies born to mums on methadone or bupe are born dependent. And if the baby is born dependent, it's a very simple process to withdraw them with oral morphine. It's not the end of the world despite the hysteria of lots of posters in this thread.
You need to get proper medical care as soon as possible. You are more likely to get into trouble with child protection services if you try to hide and manage this yourself. Front up and get some help.