The Missing Midwives report reveals that pregnant women frequently give birth at home without a midwife with only a dirty blade to cut the umbilical cord and herbs from a traditional healer to try and combat infection.
In some countries, cultural reasons mean that husbands sometimes deter their wives from seeking any help at all, leaving them to face the riskiest moment of their lives alone.
As a result, 1,000 women and 2,000 babies die every day from birth complications which could be easily prevented, the agency said.
Save the Children, which is launching a celebrity-backed campaign for more midwives, estimates that if the global shortage of 350,000 midwives was met, not only would many mums be saved, but more than a million more newborn babies would survive every year instead of dying from easily preventable problems.
Justin Forsyth, Chief Executive of Save the Children, said: "While in the UK our thoughts turn to our own mums this weekend, we must not turn our backs on the mums and babies who will die today during birth or from complications associated with it.
"No mother should face giving birth without help. It doesn't have to be complicated: someone who knows how to dry a baby properly and rub its back to help it breathe can make the difference between life and death. No child is born to die."
The report shows that the discrepancy between the developed and developing world is at its starkest at the moment of birth. In the UK, only 1 % of women give birth without trained help; in Ethiopia the figure is 94%. In the UK - where there are 749,000 births a year - there are 26,825 working midwives while in Rwanda - where 400,000 babies are born a year - there are only 46.
Save the Children notes that some progress has been made in recent years even in the poorest, most conflict-prone countries. Afghanistan is one of the most dangerous places in the world to be born but the number of midwives - although still pitifully low - has tripled within the past three years, thanks in part to midwifery colleges run by aid agencies including Save the Children.
But it warns that unless global political will and funds are pledged to plug the midwives' gap and improve access to healthcare generally, the Millennium Development Goals to cut child and maternal mortality will not be met and mothers and babies will continue to die in shocking numbers.
Forsyth added: "We are calling on rich and poor country governments to put health workers at the heart of their plans. World leaders pledged to do just that last year, but now they need to deliver the funds and political will to support this pledge. Without it, mums and babies will continue to die needlessly every day."
Save the Children's global push for more midwives - part of its "No Child Born to Die" campaign - is being backed by celebrities including former Ballykissangel actress Dervla Kirwan, X Factor star Stacey Solomon, journalist Natasha Kaplinsky and film director Gurinder Chadha who will attend a launch event in central London this morning.