My DP probably has Aspergers (undiagnosed officially but three psychologists agree and after he read about it he recognised himself and his adolescence very clearly - sadly). I recognised his traits and certainly we are a stereotypical Aspergers and non-Aspergers couple..going through divorce as a result.
That aside.
I've had two children with him and after the second which was very difficult and I had absolutely no emotional support of empathy with him I couldn't have the third child I'd always wanted. The possibility of going through that isolation again was too much.
If you go ahead, think about how a second baby adds not only a second child but more relational links. So it's not the relation between you and child that needs managing but between the child and their sibling and other parent. It can be done but sometimes it's an emotional burden for you because he isn't aware.
However, if he's open to learning and accepting that there are some things he needs to learn if he wants to facilitate his family, then he will be able to follow clear instructions on how to respond to the children.
DP and I aren't going to be together naturally, but the children are so important to him that he's been willing to work on things for their sake that he hasn't with me.
But during the pregnancy you need to make sure you have people to lean on and I'd consider lining up a therapist - being emotionally seen and heard isn't a luxury, it's something everybody needs and the partner of someone with Aspergers often lacks, to the detriment of their own health and self esteem, despite the positives that can come with being in a relationship where Aspergers features.