So I fucking hate that this is where my brain went, but my kneejerk reaction to this was: "If I do this, could it be used as evidence to charge my wife with the death of a nonexistent fetus?"
I live in the cousin-fuckingly-deep south where women are incubators and a long list of stereotypes. I could definitely see it argued in court - successfully - that an app like that was only used on my phone to try to conceal my wife's data, and the data points to one of the ways we've criminalized pregnancy.
...and that's thinking about what could happen here and now. Once Trump has had his way with our country, we'd probably just get deported to one of daddy Putin's gulags or some shit.
not to mention the reason why you're only supposed to say the word "lawyer" to cops is they literally tell you: "ANYTHING you say CAN and WILL be used AGAINST YOU in a court of law." That doesn't mean "might or maybe" or "to help you."
Track your nightly flatulence on a piece of paper too, and keep the same data on it that you put in the app. If it makes it to court claim the app was just a convient way to track other things, and let the courts discuss your farts.