In my first year at university in Nigeria, my roommate Kathy found out she had become pregnant by accident. She was 18, a promising student with her whole life ahead of her. But she wasn’t ready to become a mum and feared her family’s reaction. She tried to end the pregnancy herself – and lost her life in the process.

Eight years later, I still replay one conversation I had with Kathy, where I asked if she and her boyfriend were using birth control. She replied: “No. I don’t even know where I’d get it.”

In the aftermath of her death, questions tumbled through my head. Did our school fail Kathy by not providing better information about safe sex and contraceptives? What if Kathy had spoken up when her boyfriend said he didn’t like condoms? Could an open conversation with her parents have saved her life?

I realise now that Kathy’s death was a symptom of a much larger issue: the world is too scared to talk about teenagers having sex. And young people are losing their lives and livelihoods as a result.

I see these attitudes everywhere, from Nigeria to the UK. Parents who are too uncomfortable to have “the talk” with their kids, nurses who deny young girls contraceptives because they think they’re “too young to have sex”, education ministers who believe the best policy for addressing teenage pregnancies is a sound beating paired with expulsion rather than comprehensive sex education classes.

In Nigeria and abroad, politicians hear these cries but worry that supporting programmes that increase youth access to contraception will cost them their jobs. These fearful leaders – the very people we need to support young girls so they can improve their lives – earmark foreign aid for politically safe initiatives like abstinence-based sex-ed or programmes that only provide birth control to married women. In the worst cases, they slash funding for international reproductive health programmes altogether.

The result? Millions of young women like Kathy are left without access to birth control, pregnant too early or too often, their future plans derailed or lives ended.

If things don’t change, we’ll all face the consequences. There are 1.2 billion people in the world between the ages of 10 to 19 and most live in developing countries. This puts us on the precipice of two radically different futures.

One is where the world fails to deliver for its young people. Teenagers continue to have unintended pregnancies. Millions of girls experience health issues stemming from pregnancy and childbirth their bodies aren’t ready for, and efforts to improve gender equality are upended as teenage mothers are forced to drop out of school and face lifelong economic insecurity.

Taken at scale, this has the potential to put the economic and social progress of entire countries at risk, and has lasting implications for global trade, migration and foreign affairs.

The second scenario is where we invest in our young people so they can get reliable information about reproductive health and birth control. They decide when to have children and how many to have. They become the biggest generation of educated, empowered, working adults the world has seen. They break the cycle of poverty for their families and shape the future of their countries.

This isn’t just wishful thinking. Data shows that meeting the family planning needs of all Nigerian women who want to prevent pregnancy would increase the country’s per capita income by a third by 2030. And if all 200,000 adolescent mothers in Kenya completed secondary school and were employed instead of having children early, the country’s annual gross income would grow by $3.4bn (£2.6bn)– an amount equivalent to the entire Kenyan construction sector.

To make this second option a reality we have to act now.

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Government officials here in Nigeria are trying. In September, vice-president Yemi Osinbajo said the country must take urgent steps to avoid risky and unchecked population growth. And in 2017 our government pledged to implement reproductive health education in schools. But changing the status quo requires more than local promises.

Foreign aid helps fill the funding gaps that often prevent these intentions from becoming reality, so politicians from donor countries like the UK must think hard about where they channel investments. Their choices will determine the future of Africa’s youth, Asia’s youth, the development of the global economy and the scale of future aid needs. That means specifically supporting reproductive health programmes that meet the needs of young women: offering comprehensive reproductive health education, training providers to deliver high-quality counselling to teenagers, ensuring that a range of effective and safe contraceptives remain affordable and in stock, and destigmatising “the talk”.

Twenty years ago, the UK invested in these strategies at home. As a result, teenage pregnancy rates dropped by half. If developing countries are to achieve the same success, the world must start talking openly about teenagers having sex. Let’s learn from experience and commit to giving today’s youth and tomorrow’s leaders the information and tools they need to have safe sex, plan pregnancies and keep their lives on track. If we succeed, they’ll do more than plan their families – they’ll shape a better future for us all. And that’s the smartest investment any government can make.

Jennifer Amadi, co-founder of the Knit Together Initiative and recognised as a global leader in youth access to family planning, will speak at the international conference on family planning in Rwanda between 12 and 15 November