Almost eight million children world-wide are born with a serious genetic birth defect each year, a report shows.
Defects are more common in poorer countries
The March of Dimes health agency conducted the first comprehensive global analysis of the problem.
The report reveals at least 3.3 million under-fives die annually because of a serious birth defect.
An estimated 3.2 million of those who survive may be mentally and physically disabled for life.
Folic acid supplementation to prevent neural tube defects
Iodisation of salt to prevent severe congenital hypothyroidism
Rubella immunisation to prevent congenital rubella syndrome
Overall, the report found around 6% of babies are born with a serious genetic, or partial genetic defect.
On top of this, hundreds of thousands more are born with serious birth defects linked to exposure in the womb to alcohol, or infections such as rubella or syphilis - but these are not included in the current report.
The report said death and disability from genetic birth defects could be cut by up to 70% by introducing often simple measures, such as giving pregnancy women folic acid supplements to minimise the risk of spina bifida.
Until now the scale of this problem has not been known. The new research is based on a data from 193 countries.
The report found the overwhelming majority of babies with birth defects are born to women in poor, or middle-income countries.
The five most common birth defects, which made up a quarter of all birth defects in 2001, were:
- Congenital heart defects (1,040,865 births)
- Neural tube defects, such as spina bifida (323,904 births)
- Haemoglobin disorders, such as thalassemia and sickle cell (307,897 births)
- Down Syndrome (217,293 births)
- G6PD enzyme deficiency (177,032 births)
Dr Jennifer Howse, president of the March of Dimes, said: "Our report identifies for the first time the severe, and previously hidden global toll of birth defects.
"This is a serious, vastly unappreciated and under-funded public health problem."
The report found a number of reasons why the rate of birth defects was higher in poorer countries.
For instance, women in these countries tend to have children at a more advanced age, and marriages between blood relatives are more common.
In countries affected by malaria a greater proportion of people carry a gene that increases the risk of diseases such as sickle cell anaemia.
The report said efforts are needed to educate the community, health professionals and policy makers about how the risk of birth defects can be minimised.
Health care providers should be trained to use simple diagnostic and preventive tools that are available.
Ensuring women eat a healthy, balanced diet during their reproductive years would also make a significant impact, as would better control of infections during pregnancy.
Dr Arnold Christianson, of the University of the Witwatersrand in South Africa was lead author of the report.
He told the BBC News website: "The toll of birth defects has really been largely underappreciated over the years, and as a result has not really been included in efforts to improve child health and survival.
"There is an awful lot that even the poorest countries can do to try to prevent birth defects and the time has come for them to start implementing these measures."