And the ads sound like they're targeted on relatively tame demographic data, like a person's age, as opposed to the more private data the app collects (e.g. how often a woman has sex or where a woman is in her cycle).
And even if that sensitive data were used for targeting, I would imagine it would be for things like, "Show ads for lubricants if a person is sexually active" or "Show ads for tampons during the week prior to menstruation." Which doesn't really strike me as that privacy-invading, given the nature of the app.
I think the privacy implications get worse if the data is sold to third parties, or if it is used to make decisions that aren't tied to the data being tracked. For instance, imagine if insurance companies determined that there is a difference in risk between people who have sex frequently vs. infrequently and wanted to use this data to inform their underwriting decisions. That's where it gets scary.