I have ongoing relationship issues and am worried that because of stress my baby could end up autistic, after reading that stress causes autism?

Good time 4 therapy: It is highly unlikely that the stress you are feeling is going to cause your baby to be autistic. However, the stress and anxiety that you are going through may effect you and your ability to take care of your baby. Pregnancy often precipitates anxiety, depression and other mental health issues . So now is a good time for you to talk with a mental health professional

It's complicated: Autism is a very complex genetic issue. You must have the genetic contribution but traumatic stress can increase a baby's risk. Research suggests that 22% of the variance was due to stress during pregnancy. Talk w/ your OBGYN this but try not to worry since that will only add to the stress. I'd advise Psychotherapy to manage stress. now.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2632594/