United Nations — A startling new report by U.N. agencies and public health experts sheds light on one of the greatest threats to newborn babies worldwide: being born with low birthweight. The report, published today in the British medical journal The Lancet Global Health, says that 80% of the 2.5 million newborns who die worldwide every year are low birthweight — a terrible trend that researchers believe can be changed.

Significantly, although three-quarters of the low birthweight babies were born in Southern Asia and sub-Saharan Africa, the problem also "remains substantial" in high-income countries in Europe, North America (including the U.S.), Australia and New Zealand, the research paper says. The study was written by experts from the World Health Organization (WHO), the U.N. children's agency UNICEF, and the London School of Hygiene & Tropical Medicine.

Millions of babies at risk

In global terms, 20.5 million babies each year are born with low birthweight, defined as weighing less than 2,500 grams or 5.5 pounds. That's 1 in 7 babies worldwide. And it's not just a problem in poor countries.

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"High-income countries have seen virtually no progress," the study states, and the United States' rate of low birthweight has gotten worse in the five-year period (2000-2015) covered by the research. The report collated birthweight data on 281 million births from 148 U.N. member states.

The researchers note that they didn't set out to examine the causes of the problem. But they do conclude that in high- and middle-income countries, "factors such as maternal obesity, non-communicable diseases, higher maternal age, caesarean sections that are not medically indicated, and increasing use of fertility treatments are potential factors to address," according to Professor Joy E. Lawn, senior author of the report.

In lower-income settings, those same factors must be taken into account, but added to those are "interventions to tackle adolescent pregnancy, maternal infections such as malaria and HIV, nutritional factors e.g. the double burden of obesity and undernutrition and anemia, and environmental factors such as exposure to indoor air pollution," said Lawn, who is the director of Maternal Adolescent Reproductive & Child Health at the London School of Hygiene & Tropical Medicine.

"Low birthweight is probably the single piece of information about you that most predicts your health throughout your whole life course," Lawn added in a call with reporters. She called it "central to our vision to transforming the world."

Reducing inter-generation poverty

Another reason why tackling this problem is so vital, she said, is because it affects "adult onset of chronic conditions, which is an epidemic around the world… and perpetuates inter-generation poverty."

To be clear, thanks to consciousness of nutrition and maternal and neonatal health, average birthweights in many developed countries have increased. Newborn birthweights in the U.S. and Canada, for example, have gone up for decades, only leveling off in recent years, Today's Parent, a Canadian journal, reported.

But the dilemma of low birthweight babies persists, and how a child fares in its path to adulthood remains vexing. In richer, developed countries, infant mortality has declined, but a child in the U.S. has a 70% greater chance of dying before adulthood than in other developed countries, the journal Health Affairs revealed in January 2018. And this new study shows that low birthweight newborns continue to be a problem in the U.S.

Dr. Hannah Blencowe, the first author of the report, told CBS News, "In the U.S., you have very high pre-term birthrate." She said a lot of the issues in the U.S. are due to a high rate of medically unnecessary C-sections, among other things.

"The other issue with the U.S. is the large inequalities," Blencowe said. "If you look at the different ethnic groups and geographical distribution, that we did previously, on pre-term birth, there is a wide gap between white middle class compared to African [American] and Hispanic groups in other parts of the U.S."

Those underserved groups "face the same issues as low-income countries face, not having able to access health care," she said, adding that the problem can be turned around with investment.

The U.S. Centers for Disease Control and Prevention (CDC) provided the U.S. data for the report and reviewed the overall findings. So it is not surprising that the CDC has found similar patterns in the years after this study's data ends. In 2015, the rate of low birthweight babies increased to 6.34% among singleton births (as opposed to twins or multiple births) in the U.S., and in 2016 it rose again to 6.44%. Those increases reversed a decline from 2006 to 2014.

"This is a wake-up call"

Dr. Mercedes De Onis, a co-author of The Lancet study, said the number of neonatal deaths in low birthweight newborns can — and should — be lowered. According to Lawn, the Global Nutrition Plan of the WHO has as a key target to reduce low-birthweight newborns by 30% between 2012 and 2025, but she said "progress is really slow in high-income countries."

Dr. Victor Aguayo, UNICEF's global chief of nutrition, said most of the agency's work "focuses on low- and middle-income countries because this is where 90% of low birthweight cases occur."

"This is a wake-up call to governments, to the U.N., and all partners to close three gaps," Lawn said, outlining three areas that need to be addressed:

Care gap – 20.5 million low-birthweight babies at risk of inadequate care. Prevention gap – Increase progress to reduce the rate of low birthweight babies. Data gap – All babies should be weighed at birth and the data entered in national records.

"We owe it to every newborn around the world, to their families and to every country to close these three gaps" in order to "turn off this tide of ill health," Lawn said.

"These most vulnerable babies must not be left behind," the report concludes.