Throughout the country, more and more babies are coming early. In 1981, fewer than 1 in 10 babies were born prematurely. Today, it’s 1 in 8 –– more than 530,000 preemies each year, including about 1,500 in Rhode Island.

A lot of preterm infants die, and that’s the main reason the United States has one of the highest infant mortality rates in the developed world. Babies who died of causes directly related to prematurity account for a growing proportion of infant deaths, reaching 36.5 percent in 2005. The persistence of premature births has stalled progress against infant mortality.

Journal photo / Kathy Borchers

Cristina DiChiera holds her baby, Violetta, at Women & Infants Hospital in May in Providence, R.I. DiChiera had no risk factors and did everything right during her pregnancy, but went into premature labor at 26 weeks. Violetta was born on April 12 weighing 2 pounds, and went home in July.

But much more is involved than early death. The surviving babies need days to months of intensive care, at costs that can run into hundreds of thousands of dollars, sometimes millions — expenses that contribute to the price of health insurance for everyone and to the cost of public assistance.

In one recent year, the second most expensive case that Blue Cross & Blue Shield of Rhode Island paid for was a premature baby. Nationwide, the single most expensive condition per hospital stay is respiratory distress syndrome, an illness of infants, mostly preemies. Preterm and low-birth-weight infants account for half of all hospital costs for infants and one-quarter of all medical expenses among children.

Then, preemies often have disabilities requiring additional help as they make their way through life. The Institute of Medicine estimated that in 2005, prematurity cost American society $26.2 billion in medical care, early intervention services for preschoolers, special education for disabled children and lost productivity. That figure encompasses only the first few years of life — not the lifelong consequences.

Scientists trying to fathom the underlying causes of premature birth have identified factors so vast, varied and intertwined that they seem to reflect America itself.

Our astonishing technological capabilities save the lives of many a preemie. But that success paves the way for obstetricians to end complicated pregnancies early, knowing the baby will almost surely survive. New treatments enable infertile couples to bear children, but that can lead to multiple births, more than half of which are premature. Even among single births, infertility treatment raises the risk of premature delivery.

Social trends encourage women to have babies later in life, when they are more susceptible to health problems that can lead to an early delivery.

Social problems contribute heavily, too. Poverty, inadequate education, poor nutrition, teenage pregnancy, domestic abuse, drug abuse, racism — each has been linked to premature birth. African-American women have much higher rates of premature births, possibly because of a combination of genetic susceptibility and social factors, including the stress of racism.

Meanwhile, a low-level ill health afflicts wide swaths of society, rich and poor: smoking, poor eating habits, lack of physical activity, obesity, high blood pressure, diabetes and chronic stress –– any of these can threaten a pregnancy.

Biology is also important. Infections and genetics each play a role in ways that scientists are still trying to untangle.

Many mysteries remain. In close to 40 percent of premature births, no one knows why they happened.

ffreyer@projo.com