The UK has been ranked the 23rd best place to be a mother - falling behind countries including Ireland, France and Estonia.
Save the Children 's State of the World's Mothers report saw the UK fall from joint 10th in last year's list of 176 countries.
Finland, Sweden and Norway claim the top three slots respectively in the Mothers' Index.
But for the first time, countries in sub-Saharan Africa - where 10% to 20% of mothers are underweight due to poor nutrition or underage pregnancy - take up each of the bottom ten places in the annual list.
Ireland is ranked at number 20, while the US is at number 30, Germany is at number nine and France is at number 16.
The Democratic Republic of the Congo was named in the report as the world's toughest place to be a mother.
Countries relative success or failure in saving the lives of mothers and newborn babies is analysed in compiling the index.
It also assesses indicators of maternal health, under-five mortality, levels of women's education, income and political status.
At number 23, the UK has fewer women in Parliament and higher maternal and infant mortality rates than much of Europe, the charity said.
Poverty and inequality also contributed to the UK's ranking, as women with partners who are unemployed are six times more likely to die from maternal causes than those with partners in work.
The charity said one million babies across the globe die each year on the day they are born - or two every minute.
A child in the developing world is seven times more likely to die on its first day than a baby born in industrialised nations.
Justin Forsyth, chief executive of Save the Children, said: "Overall the world has made unprecedented progress in reducing child and maternal deaths.
"But within this progress there are two big challenges: newborns and malnutrition.
"We can end child and maternal mortality in our generation - by using tried and tested interventions to stop mothers and babies being lost from what should be simple preventable causes."
Top 25 countries in the Mothers' Index:
18. New Zealand
23. United Kingdom
24. Czech Republic