It's a hard call
I think the first thing you should do is talk it through with your partner and a counsellor perhaps as well. And give yourself time - can you afford to keep it on ice?
I know when we first fell pregnant with DS we were dead keen to donate any leftovers we might have after finishing our family. But after he was born we felt completely different. The baby changed from being a hypothetical to a reality and I just wasn't sure if I could give up a child like that (I know it's not quite the same thing, but anyway). I personally hate the idea of destroying them and would rather they went to research or lab practice, but DH is deadset against that. Luckily we're not in the position of having to make that choice right now and still want to expand our family, so with any luck we won't have to.
All the best making your choice