Menstrual cycle

Although the palm-sized device looks nothing like a womb, fallopian tubes and ovaries, the researchers say it should help with understanding diseases of these organs and tissues.

It also provides a novel way to test new treatments.

The work is part of a project to create the entire human "body on a chip".

The ultimate goal would be to take cells from any given individual in order to create a personalised model of their body to test drugs and treatments on, Nature Communications reports.

This is no doubt why a provision in the country's labour law that allows female workers to take off one day a month is known as Mother's Day, even though it applies to all women, whether or not they have children.

The legal definition is not precise - women can take the day when they want and do not have to provide any medical justification, leading some to question the provision.

"I think it's a good law because women go through a lot when they are on their menses [periods]," says Ndekela Mazimba, who works in public relations.

There are thought to have been as many as 200m downloads of period tracking apps worldwide.

But a leading UK medical royal college has warned that women should not rely on them as a form of contraception.

And privacy campaigners say users should be wary of what data they might unwittingly be sharing when they download some apps.

A search for period tracking apps will quickly bring up dozens of offerings - some with charts, others illustrated with pink tulips or lilac flowers.