Period tracking apps help you track your menstrual cycle, so you know when to expect your period. They’re growing in popularity worldwide, with the three most popular ones racking up over 250 million downloads between them. But studies show that some women might also be using them to avoid getting pregnant.

One of the apps, Natural Cycles, has been approved in the US to be used as a contraceptive. The company claims it is 93% effective at preventing pregnancies, when used perfectly. So why are more people turning to these apps? Are they safe to use as a contraceptive and what are the risks?

Sexologist Rayka Kumru from Turkey explains why these period tracking apps are becoming so popular and the privacy concerns around using them. Dr Francesco Rampazzo, a lecturer in Demography at the University of Oxford, tells us more about where period tracking apps are getting the most downloads.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Hannah Gelbart Producers: Chelsea Coates, Benita Barden and Emilia Jansson Video Journalist: Baldeep Chahal Editor: Harriet Oliver

Violence has flared up again in Syria, this time in the southern province of Suweida. Fighting has broken out between the government forces and two minority groups: the Druze and the Bedouins. It’s not the first time that the stability of the country has been shaken since the fall of dictator Bashar al-Assad last December. But it signals the challenges the new government faces - not just from internal violence, but from its neighbours. Israel launched air strikes on Suweida and the Syrian capital, Damascus, and says it will only hold a US-backed ceasefire if the Druze are protected. So, what’s behind this conflict - and what does it mean for the future of Syria?

We speak to BBC Monitoring journalist Tess Mallinder Heron, to explain who the different groups involved in the fighting are and what’s behind the dispute. And we hear from our BBC Middle East Correspondent in Damascus, Lina Sinjab, who tells us what life has been like for people in Syria since the fall of Assad’s regime - and how the new government is trying to maintain control in Syria.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Hannah Gelbart Producers: Emily Horler and Chelsea Coates Editor: Verity Wilde

Dozens of coastal cities — from Jakarta to Manila — are sinking at a worrying speed. Climate change, too much water being pumped out of the ground for drinking and the type of land cities are built on all contribute to the problem. But people around the world are coming up with innovative ways to tackle this.

Aghnia Adzkia, a BBC journalist based in Jakarta, shares why Indonesia’s capital is particularly vulnerable, and how people there are trying to protect themselves. BBC climate correspondent Georgina Rannard explains the link between climate change and rising sea levels. And we hear from people helping their local communities to adapt, such as architect Kunlé Adeyemi, who designed a floating school in Lagos.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Iqra Farooq Producers: Chelsea Coates, Mora Morrison and Maria Clara Montoya Video Journalist: Adam Chowdhury and Jem Westgate Editor: Verity Wilde

Wafcon — or the Women’s Africa Cup of Nations — is heating up. Ahead of the final this Saturday in Morocco, only four teams out of twelve remain: Nigeria, South Africa, Morocco and Ghana. The tournament first took place in 1991 and since then, it’s taken off, with the Confederation of African Football reporting that more that more people are tuning in to watch every twist and turn of the competition. It’s given football stars from across the continent a chance to show off their skills on the world stage - and put the spotlight firmly on the women’s game.

So which team will get to hold up the cup this year? And how is the tournament changing attitudes to women’s football across Africa?

BBC Africa sports reporter Celestine Karoney explains how the tournament has changed over the years and what challenges female players still face. And the BBC’s Sara Menai updates us on the latest from the tournament as the last four teams battle it out for the cup.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: William Lee Adams Producers: Mora Morrison and Chelsea Coates Editor: Emily Horler

If someone talks about Cuba does it make you think of cigars and classic cars? Or maybe you think of limited freedom of speech and Che Guevara?

We’re talking about Cuba because its minister for Labour, Elena Feitó Cabrera, was forced to resign after she said there was no such thing as ‘beggars’ on the island. What’s the situation with homelessness?

We’re running through some of the top claims we’ve seen about Cuba online with Will Grant, our Cuba Correspondent, and break down how much truth there is behind them.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: William Lee Adams Producers: Emily Horler and Benita Barden Editor: Verity Wilde

Do you find yourself tossing and turning for hours whilst struggling to fall asleep? Or are you out like a light the minute your head touches the pillow? Genetics and environment can play a big part in how easy (or not) you find sleeping.

BBC science journalist Caroline Steel tells us more about what happens to our brains when we sleep and what exactly happened when she visited a sleep lab for a BBC documentary. Medical doctor and sleep expert Dr Jonathan Tham gives us his top tips on getting a good night’s sleep.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Iqra Farooq Producers: Emilia Jansson, Josh Jenkins and Julia Ross-Roy Video Journalist: Jem Westgate Editor: Verity Wilde

Oceans make up more than 99% of the Earth’s habitats by volume — yet less than 20% of them have been explored. Some even say it’s easier to send astronauts into space than it is to reach the ocean floor. Only a handful of people have ever reached the deepest part of the ocean - known as the Challenger Deep in the Mariana Trench in the Pacific Ocean. So, why is it so difficult to get there? And what new tech is helping us uncover the ocean’s secrets?

The BBC’s Climate and Science correspondent Georgina Rannard explains why we know so little about what’s going on in the deepest parts of the ocean and some of the discoveries that have been made about this mysterious part of our world.

Archive courtesy of British Pathé.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: William Lee Adams Producers: Baldeep Chahal, Julia Ross-Roy, Emily Horler and Emilia Jansson Video Journalist: Baldeep Chahal Editor: Verity Wilde

Across cultures, weddings are usually a big event. Lots of us look forward to dressing up and dancing the night away with the person we love — but what if you kept all the festivities and got rid of the romance? Well, some young people in China are doing exactly that, by looking online for a ‘marriage buddy’. They pretend to be together to please their families, but aren’t actually legally married. So, why are they willing to go to such lengths to meet societal expectations? And how does it all work?

Wanqing Zhang from the BBC’s Global China Unit talks us through the process — and explains the pressure put on young people in China to tie the knot. And we hear from Linda, a young woman in China who tells us why she’s decided to find a marriage buddy.

Instagram: @bbcwhatintheworld Email: whatintheworld@bbc.co.uk WhatsApp: +44 330 12 33 22 6 Presenter: Iqra Farooq Producers: Chelsea Coates, Mora Morrison and María Clara Montoya Video Journalist: Baldeep Chahal and Jem Westgate Editor: Julia Ross-Roy