Women who use the pull-out method instead of condoms are also at risk for sexually transmitted infections, such as Chlamydia and HIV.

Some of those pregnancies occurred when women weren't using their chosen contraception and instead relied on a condom or the pull-out method.

Along with participants who used the pull-out method, African American and poor women were more likely than others to have had an unintended pregnancy.

Dr Dude's findings revealed that 31% of young women in America aged between 15 and 24 had relied on the pull-out method at least once.

Apparently, these women had never heard the old joke: you know what you call a couple who use the rhythm and pull-out methods?