Should I try to talk about this to DH?

I like Indyan's advice. I also suggest that when you talk to your husband. find a good comfortable atmosphere. and slowly ask him in lightly happy/teasing voice how much he loves your child (both your child).

ask him questions like do you think our child will be most beautiful in world? would he have your features more or mine? etc etc

get him to think about both your child more. talking about his sister and her child and comparing to yours is risky but depends a lot on how close you two are and how comfortable you two are in talking about anything... and especially how you two resolve issues when they surface. take into consideration all of this and only if you feel he will take your concern seriously and try to improve, then try to talk openly.

otherwise keep talking abt both your child and get him excited about it. good luck!