The CEO of the Gates Foundation says a wave of progress rippling through China and India could slash poverty in Africa - if women lead the way

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A family eats 'Fou Fou' Kasava and fish in the West Lake Edward village of Lunyesenge in the Democratic Republic of the Congo.

• The Gates Foundation released its second annual Goalkeepers Report today, a project that's meant to keep yearly tabs on the 2030 Sustainable Development Goals from the United Nations.
• In the report, Bill Gates and his team applaud the fact that hundreds of millions of people have risen out of extreme poverty in the past couple of decades, but warn the progress may not continue.
• Keeping more women in school, and letting them decide when they want to have kids would both help a lot.

There's a crude but simple way to measure extreme poverty around the world. Look at how many people are living on less than $1.90 a day. The higher the number, the worse-off we are.

The good news is that the number of people getting by on that much has been steadily falling for decades, with over a billion people surging over the mark since 1990, according to the World Bank.

China's on track to nearly eliminate this income bracket by 2030. So is India.

Now, it's time for sub-Saharan Africa to follow suit, a new report from the Gates Foundation argues.

The Goalkeepers report is an annual check-up that's meant to keep tabs on the United Nation's sustainable development goals, which aim to end poverty, hunger, and generally improve people's lives around the world by 2030.

In this year's Goalkeepers report, the normally optimistic Gates Foundation says the wave of poverty-busting prosperity that rushed over China in the 1990s and then India in the 2000s, lifting more than 750 million people in those countries above the $1.90-a-day mark, is not yet guaranteed on the African continent.

"The big message is that progress is possible, but it's not inevitable," Gates Foundation CEO Sue Desmond-Hellmann told Business Inside. "We really need to have a third wave, and it needs to happen in sub-Saharan Africa."

[Read More: The CEO of The Gates Foundation says we're approaching a dangerous tipping point in global poverty. We still have time to reverse it.]

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Both China and India have complicated economic success stories that are nowhere near complete.

But lower fertility rates are arguably linked to better incomes in both countries: China's birth rate tumbled from 5.7 per woman in 1960 to 1.6 in 2016, while India's went from 5.9 to 2.3, according to World Bank data. At the same time, those two countries became global economic powerhouses. The gains meant more people could feed and send their kids to school, ensuring the betterment of coming generations.

"It's fantastic to see the kinds of gains in health and education we've seen," Desmond-Hellmann said. "But the worry, the peril, is that more babies are being born in the places where it's hardest to live a healthy, productive life."

In the years to come, many of the poorest babies (and 86% of the world's extreme poor) are going to be born in a cluster of sub-Saharan African countries, particularly in two specific nations: The Democratic Republic of the Congo and Nigeria. Those two countries alone could account for nearly half of the world's poorest people by 2050, according to Gates Foundation estimates. Both of their birth rates have barely budged since 1960.

Much of the poverty there will be driven by rapid population growth, more than doubling the number of people in both countries. The staggering increase could be altered, though, if women and girls get to better choose how many children they have from the get-go.

Women in Africa are currently having an average of about .7 more children than what they'd ideally want. If they got to decide how many kids they birthed, having one or two less, the projected rapid population growth could decrease 30% by 2100, according to the foundation. That would make everyone healthier, smarter, and richer too.

"You want those young people to have healthy, productive lives," Desmond-Hellmann said. "Nutrition, and early childhood nutrition, are extremely important."

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A malnourished refugee mother and child in a ward of the Medecins Sans Frontieres Hospital in the Dagahaley refugee camp on July 22, 2011 in Dadaab, Kenya.

"We think investments in voluntary, modern contraception for women who want to decide when she has her children and to space her children, that's a really important investment that we could make as a foundation," Desmond-Hellmann said.

The $50 billion-plus Gates Foundation has spent more than $15 billion on projects in Africa to date, but much of the push has been for more vaccines, as well as in HIV and malaria prevention and treatment. While the foundation is still researching new treatments for HIV and providing vaccinations in 73 countries around the world, some of the foundation's health focus is shifting to baby-making.

Desmond-Hellman says the Gates Foundation will now invest more in family planning and contraception.

It's arguably filling a needed void at a time when the US is dialing down its own family planning foreign aid. Just days after President Trump took office in January 2016, the administration reintroduced the decades-old Mexico City Policy, which essentially zeros out American dollars to any NGOs that might even mention the word abortion when they're counseling women.

Practically, it means that women living in remote, impoverished areas have less access to all kinds of contraceptive care and family planning advice. In Madagascar, even though abortion is illegal, the policy is still preventing many low-income women from accessing free contraception like implants and IUD devices, as NPR reported last year.

Without access to contraception, it's harder for young girls to stay in school, or help plant crops at home. More access to contraception "would enable more girls and women to stay in school longer, have children later, they could earn more as adults, and they could invest more in their children," as Desmond-Hellmann put it.

But only if they have a choice.