Most birth defects occur in poor countries, where babies can languish with problems easily fixed or even prevented in wealthier nations, according to research released Monday by the organization.
But the researchers said some innovative programs in Iran and Chile show that effective preventions don't have to be costly.
Indeed, about 70 percent of birth defects could be either prevented, repaired or ameliorated, they concluded.
"We were surprised by the toll," said epidemiologist Christopher Howson with the March of Dimes, which sponsored the five-year project after doctors complained that birth defects often are ignored as a public health problem.
"It's like this monster that rises out of the mists" only after infant mortality from other causes drops, he said.
Specialists said the report focuses much-needed attention on a concern of every parent-to-be.
"Most people think of birth defects as something that is not preventable," said Dr. Jose Cordero, the U.S. assistant surgeon general and birth defects chief at the Centers for Disease Control and Prevention. "There are great opportunities to ensure that babies are born healthy."
Some 7.9 million children a year are born with serious birth defects caused at least partly by a genetic flaw, such as heart defects, spina bifida and other neural tube defects, sickle cell anemia and Down syndrome.
Undoubtedly hundreds of thousands more are born with defects caused not by genes but by post-conception problems: mothers infected with rubella or syphilis, which can damage their babies' brains; certain medications or alcohol; lack of dietary iodine. But too few countries count those defects for a good estimate.
At least 3.3 million children under age 5 die each year because of birth defects, and millions more are mentally or physically disabled.
Prevalence ranges from a high of 82 defects per 1,000 live births in Sudan to a low of 39.7 per 1,000 in France. The researchers cautioned that the data aren't precise enough for detailed country-by-country comparisons — but cited poor maternal health care, a higher percentage of older mothers and greater frequency of marriage between relatives as leading risks in low- and middle-income countries.
Additionally, populations from Africa, the Eastern Mediterranean and Southeast Asia are most at risk of the common inherited diseases thalassemia, sickle cell and the metabolic disease G6PD, regions less likely to offer genetic testing that reveal at-risk couples.
The report takes no stand on abortion. But it also found that Down syndrome is roughly twice as common in poorer countries, which typically lack prenatal testing, while half of affected pregnancies in Western Europe are terminated following prenatal diagnosis.
Every mother-to-be has about a 5 percent chance of having a baby with a serious birth defect, the so-called "background rate," explained Dr. Arnold Christianson of South Africa's University of Witwatersrand, who co-wrote the report.
That risk can rise or fall, depending on a host of circumstances: Does she take folic acid, a nutritional supplement that fights neural tube defects? Is she vaccinated against rubella? Does she have uncontrolled diabetes or other pregnancy-harming illnesses? Is she well-nourished? Are her pregnancies spaced far enough apart?
"If mom can be as fit and well as possible at the time of conception, it reduces the risk of a birth defect," Christianson said.
Among the report's recommendations:
--Improved health care for all women, with special emphasis on pregnancy nutrition.
--Improved family planning and birth-defect education. In Johannesburg, surveys show less than 40 percent of African women know what Down syndrome is, much less that their risk rises with pregnancies after age 35, Christianson said.
--Proper care of affected babies. In South America, for example, 55 percent of babies with Down syndrome die before their first birthday. Median U.S. survival is age 51, up from age 3 in the 1960s thanks to improved care.
"Care is an absolute," Howson said. "Prevention is the ideal."
And prevention can be cheap: Fortifying grain with folic acid costs about a penny per year per person, Cordero said.
In 2000, Chile added enough folic acid to wheat flour to cause a 40 percent reduction in neural tube defects. The U.S., with lower fortification levels, saw a one-third drop.
Even gene tests can be relatively inexpensive. The report cites Iran which, faced with skyrocketing costs for thalassemia care, in 1997 began giving couples a $5 gene test prior to marriage. Some separate if both carry the disease-causing gene, but they also can opt for fetal testing if they choose to conceive. By 2001, more than 2.7 million prospective couples had been screened, 10,298 at-risk couples identified and counseled — and thalassemia births had fallen to 30 percent of the expected rate.