My SIL is pregnant with her third. Everything is going well, and she is likely to have a healthy baby. But she is very anxious that something might go wrong, in parts because with my third pregnancy things went "wrong" (ds has a type of dwarfism) and so she is a bit superstitious about third pregnancies.
Now because of ds's history I've kind of become the family expert on prenatal tests, diagnosis etc, even though my knowledge is very limited. And so my SIL and my mum try and get me to say to them that because the scans have all been fine so far (she's in week 25 or so) that it is certain that all will be well. And I do tell them that it is likely that the baby will be healthy, but I just can't bring myself to say that it is certain.