I actually found myself afflicted with that superstition recently! I'm not normally, but the kids' stepmother was having a baby (she's no longer married to their dad, the kids are referring to the baby, who shares no biological or legal connection to them, as their stepsister) and as there is approximately a zero percent chance that she'll ever have another one, or even would've had another pregnancy if this one didn't work out, I found myself balking at the idea of talking about getting baby shower presents before the kid actually showed up.