The lives of more than a million babies a year could be saved across the developing world if mothers were given access to simple, low-cost health measures such as vitamins, antimalarials and aspirin, a new analysis has found.

The study, focused on the “silent public health disaster” of babies being born “too small or too soon”, comes as the United Nations warns that progress on reducing newborn deaths and stillbirths has flatlined since 2015, and that patchy, underfunded antenatal care is partially to blame.

The authors of the analysis, published in the Lancet, estimate that 476,000 newborn deaths and 566,000 stillbirths could be avoided every year if a handful of predominantly antenatal measures were fully implemented in 81 low- and middle-income countries.

Globally, the number of neonatal deaths – babies who die within 28 days – more than halved in the three decades between 1990 and 2020, from 5 million to 2.4 million. But across the developing world, particularly in sub-Saharan Africa and southern Asia, the numbers remain high.

A UN report released this week shows that the rate of progress has stagnated since 2015 due to decreasing investment, with each year since bringing more than 2 million newborn deaths and 1.9 million stillbirths (classified by the World Health Organization as babies who die after 28 weeks of pregnancy).

“If we wish to see different results, we must do things differently,” said Dr Anshu Banerjee, the WHO’s director of maternal, newborn, child and adolescent health and ageing. “More and smarter investments in primary healthcare are needed now so that every woman and baby, no matter where they live, has the best chance of health and survival.”

Many, if not all, the measures recommended in the series published in the Lancet are already used in high-income countries, from helping pregnant women to stop smoking, to giving them aspirin when at high risk of pre-eclampsia. But they are not used systematically in many places, particularly in countries with health systems under huge pressure from humanitarian emergencies, such as Afghanistan or South Sudan.

The UN report found that less than 60% of women in the worst-affected countries received even four of WHO’s recommended eight antenatal checks.

Despite the scale of the challenge, the cost of rolling out the measures across the 81 countries would be about $1.1bn (£870m), say the authors, an amount described by one as “a fraction” of what other health programmes receive. Yet the impact could be huge, they argue, potentially preventing 5.2 million babies a year from being born either pre-term, small for gestational age or with low birth weight (defined as less than 5.5lb).

The authors – a group of professors specialising in various aspects of child or maternal health – coin a new umbrella term for these babies: small vulnerable newborns, or SVNs. They calculate that, of the 135 million babies born alive in 2020, one in four (35.3 million) would have met the criteria of being SVN.

“Our first ever estimates on this topic show that the problem of small vulnerable newborns is larger than previously realised and is a silent public health disaster affecting the whole life course, reducing human capital and impeding national economies,” said Joy Lawn, co-lead author and professor of maternal, reproductive and child health at the London School of Hygiene & Tropical Medicine.

Lead author Per Ashorn, professor of paediatrics at Tampere University in Finland, called on national governments, as well as partners and donors, to act and invest as a matter of urgency. “Despite several global commitments and targets aimed at reducing SVN outcomes since 1990, every fourth baby in the world is ‘born too small’ or ‘born too soon’,” he said.

“Our series suggests that we already have the knowledge to reverse the current trend and save the lives of thousands of babies a year at a cost of $1.1bn, a fraction of what other health programmes receive. We need national actors, with global partners, to urgently prioritise action, advocate and invest.”

In 2020, the authors calculate, more than half of all neonatal deaths worldwide were attributable to the babies being SVNs. “By not addressing this priority, we are jeopardising our collective future,” they write.