I haven't been in that situation, but isn't the cake for a party or family gathering, to reveal to them? I didn't think the cake was meant to reveal to the actual parents. That IS putting a lot of secrecy on you. By the way, I was curious whether there were gender-reveal etiquette. It seems that this event sometimes prompts a party that is not quite a shower? Or perhaps it's presented at the actual shower. Since this is a third baby, I have no idea. The showers I've contributed for have typically been for a first child, with a baby gift given for additional children after their birth, the shower fulfilling the need to get the more expensive baby provisions that can be used again. This sounds like a question only your sister-in-law can answer. I can't imagine wanting to find out from someone other than my doctor.