At age 73, Mick Jagger is about to become a dad again for the eighth time — this time with girlfriend Melanie Hamrick, who is a 29-year-old ballerina.

We don't know if she used a fertility app and the pregnancy was planned, or maybe she used a fertility app incorrectly and it was unplanned.

There may have been no fertility apps involved at all, but for many young women, these digital menstrual-cycle monitors are a 21st century solution to the (notoriously unreliable) rhythm method.

Fertility apps enable women to monitor their menstrual cycles, but the digital programs have been getting a bad rap lately.

The Department of Family Medicine at Georgetown University did an exhaustive study of fertility apps and teased out the top 40 from around 100 that are currently available.

From that pool they found only Ovulation Mentor, Sympto.org, iCycleBeads, Lily and Lady Cycle had either a perfect score on accuracy or no false negatives.

But if you are going to rely on these, the study authors point out, learning everything you can about the app is essential.

To either achieve or avoid pregnancy, it’s best to pair the app with another method. To check for optimal fertility, taking your temperature is smart — it rises when ovulation occurs.

And to avoid pregnancy, there's always abstinence or contraception.