The under-five death rate remains too high in the developing worldResearchers say just nine of 137 developing countries will achieve ambitious targets to improve the health of women and children.
The analysis in The Lancet updates previous estimates of progress on the fourth and fifth Millennium Development Goals (MDGs).
The experts predict that no country in sub-Saharan Africa will meet the goals to dramatically reduce deaths by 2015.
But they say progress is speeding up in most countries.
The targets were set by world leaders in 2000. MDG4 aims to reduce the death rate for children aged under five by two-thirds between 1990 and 2015.
MDG5 states an ambition to cut deaths among pregnant women and new mothers by three-quarters during the same timescale.
The researchers from Seattle estimate there were 7.2m infant deaths around the world in the past year - compared with 11.6m in 1990.
China, Rwanda and Botswana were praised for "substantial acceleration" in tackling child mortality in the past decade.
Intervention strategiesThere were 273,500 maternal deaths, of which 56,100 were related to HIV.
In 1990, an estimated 409,100 women died during pregnancy or childbirth.
The highest level of maternal death is seen in Eritrea, Liberia and Afghanistan. The lowest is in Iceland and Austria.
Countries making slower progress on the infant death target include Nigeria and Ethiopia.
The authors said 23 countries in sub-Saharan Africa were unlikely at the present pace to achieve MDG4 before 2040.
"Many aspects of health systems limit the scale-up of child and maternal interventions," they said.
"Nevertheless, some intervention strategies can be delivered without a health system that has the capacity for referral and emergency management.
"These include vaccination, distributing insecticide-treated bed nets, vitamin A supplementation and deworming."
They praised India for "promising and substantial" progress in reducing maternal mortality during the past five years.
The authors concluded: "The MDG targets have helped rally donors to recognise the urgent need for further investment.
"Even with major accelerated efforts, most countries are unlikely to achieve both targets.
"Although some might see this as a failure of global health action, it is perhaps more important to keep track of whether the pace of progress for children and mothers has improved."
A year ago, governments around the world pledged £25bn to reinvigorate efforts on both targets.
But the Lancet paper says the potential for delivering the aid is "unclear", because aid money for health has been growing at a slower pace in recent years.
Midwife trainingThe authors acknowledge estimating the death rates is contentious, and that their work has triggered a "vigorous academic debate on measurement strategies".
In an accompanying comment, global health experts Peter Byass and Wendy Graham said: "Numerical assessments against the MDGs are inevitably processes that are plagued by poor and missing data.
"It is self-evident that the greatest numbers of avoidable deaths happen in some of the world's largest countries."
A report by the Partnership for Maternal, Newborn and Child Health (PMNCH) - also released on Tuesday - says some of the world's poorest countries have pledged £7bn of their own resources to try to reduce the death rates.
Bangladesh has committed to train 3,000 midwives by 2015, while Congo has promised to provide free obstetric care, including Caesarean sections.
