If we're worried about global birth rates, we must address the fact that women across the world do not have full reproductive freedoms

Around the world, reproductive rights and choices are under siege. Small but organised and vocal groups would prefer that we return to a time when women had no control over their bodies or their lives.

We cannot let that happen. And so, we cannot sit idle; we have to unite and mobilise. We have to be better organised, bolder and far more vocal than those who oppose our mission to ensure rights and choices for all.

UNFPA, the United Nations sexual and reproductive health agency, today released its annual State of World Population report, The Power of Choice. This report is timely because it is about rights and choices, or a lack of them, and what that means for women, for couples, and for countries’ prospects for economic and social progress.

Most importantly, the new report makes the case that choice can change the world. Choice is about having the power and the means to make your own decisions about whether, when or how often to have children, and how that power affects other choices in life.

In countries where birth rates are high, choices are constrained not just by a lack of quality contraceptive options, but also by factors such as child marriage. About 95 per cent of births by adolescents occur in developing countries, and nine in 10 of these births occur within a marriage or union.

Even in countries where birth rates are low, like the UK, choices may be constrained. Economic factors, such as the high cost of child care, or the high opportunity cost of leaving a career to start or expand a family, are just some of the main reasons why women are unable to exercise their rights in wealthier countries.

As a result, in many countries with high birth rates, women are having more children than they want, while some women in many countries with low birth rates are having fewer children than they want.

The report also shows that not long ago, around the world, there was generally a high birth rate. But it all started changing in England and elsewhere in Europe around the Industrial Revolution, when couples realised they had the information and power to limit their family sizes and that fertility could be a matter of conscious choice.

What happened then set off a global demographic transition, where more and more countries started moving from high birth and death rates to low birth and death rates. That transition, however, started at different times and has moved at different speeds in different parts of the world. So today, there isn’t just one birth rate. There are many, and the vastly different rates among countries signal that choice is not yet a reality for all.

Regardless of whether the birth rates are high or low, it can mean challenges for countries’ economies, institutions and prospects for the future.

Countries with lower birth rates may struggle with maintaining a large enough labour force to fuel their economies or to fund social security systems for ageing populations.

The report calls on countries with high or low birth rates to confront their demographic challenges through expanding choices.

Making sure that child care is affordable, for example, is one action that a country with low birth rates can take to expand choices because it can enable women to have children without giving up their careers.

Other obstacles in low birth rate countries include uncertain labour markets. Where young people are uncertain about their future wellbeing, many will choose to delay having a family.

Paid parental leave for men and women, alignment of school and work schedules, flexible work hours and affordable housing can also make a big difference to a woman who wants to start a family.

Women should not be constrained by these dilemmas of motherhood.

Our new report comes at a time of uncertainty for reproductive rights and choices. We must push back.

Choice can change the world. And choice can be a reality everywhere, sometimes with simple policy changes that can open doors for women to have as many – or as few – children as they desire.

Dr Natalia Kanem is the executive director of the United Nations Population Fund, the UN’s sexual and reproductive health agency