Data from those apps is really valuable from a marketing perspective.

The case with least value is selling it to P&G or whoever just to track how much market share do they have.

If you put a tracker on it (facebook, for example) you can build a custom audience on top of it and promote/sell whatever you want related to reproductive healt and/or sexuality. Not just women.

You could be a little evil and sell women tampons before they have menstruation.

You could be evil and build a custom Facebook audience with users from your app and make money selling them stuff using a retargeting bid (since they are part of your audience).

Or you could be very evit and target partners of women whe ceased to use your app for more than, say, 3-4 months and show ads for DNA paternity tests (which you don't sell, but someone else does and gives a referral fee for it).

Or you could have very, very evil and build an audience around partners of women who might be pregnant, capture the clicks to build another audience (this time yours) and sell porn, tinder, dating/e-whoring, and divorce advice for a fee. Will work because this is a retargeting list (you already marked them as your customers, so bidding will be low for the ads).