Do interracial couples have a greater risk of miscarriage?

No reason to worry. An interracial baby has no reason to be less physically healthy before, during or after birth. And it is a wonderful thing that social acceptance has improved greatly in recent decades so that the child has a greatly reduced risk of social stigma. However, it is still not zero. Of course children face bullying for a variety of reasons, so this may not even add to that concern. Congratulations!
Pregnancy Myths. Nope. There is no truth to that myth.