Fifteen million babies are born prematurely each year, and the United States fared badly in the first country-by-country global comparison of premature births, which was released Wednesday by the World Health Organization and other agencies.
Although American hospitals excel at saving premature infants, the United States is similar to developing countries in the percentage of mothers who give birth before their child is due, the study’s chief author noted. It does worse than any western European country and considerably worse than Japan or the Scandinavian countries.
That stems from the unique American combination of many pregnant teenagers and many women over 35 giving birth, sometimes to twins or triplets implanted after in vitro fertilization, the authors said. Twins and triplets are often deliberately delivered early by Caesarean section to avoid the unpredictable risks of vaginally delivering multiple full-term babies.
Also, many American women of childbearing age have other risk factors for premature birth, like obesity, diabetes, high blood pressure or smoking habits. And the many women who lack health insurance often do not see doctors early in their pregnancies, when problems like high blood pressure or genital infections can be headed off.
Seeing similar problems simultaneously in Africa and the United States “is really a tale of two planets,” said Dr. Joy Lawn, director of global policy for Save the Children and the report’s chief author.
The report, three years in the making, is the first to compare premature birthrates in 184 countries. It was produced jointly by the W.H.O., Save the Children, the March of Dimes and the Partnership for Maternal, Newborn and Child Health, which has more than 400 member organizations. Other contributors include nearly 40 major American, European and United Nations health and foreign aid agencies and foundations.
The report’s conclusions about the United States are similar to those in a 2009 report by the federal government, which found that high rates of premature birth are the main reason this country has infant mortality rates higher than those of other wealthy countries.
Very poor countries have high rates of premature births for different reasons — women have many babies, adolescent girls get pregnant at even younger ages, and infections that can trigger early labor are more common.
Nine of the 11 countries in which 15 percent or more of all births are preterm are in Africa; the other two are Pakistan and Indonesia.
The United States shares the 12 percent range with Kenya, Turkey, Thailand, East Timor and Honduras, meaning one in 9 births is early. The rate in the United States has risen 30 percent since 1981.
Most European countries, Canada and Australia are in the 7 to 9 percent range.
While agreeing that the United States does poorly compared with Europe, Dr. Alan E. Guttmacher, director of the National Institute of Child Health and Human Development, took issue with equating it to Africa.
African data is shakier, said Dr. Guttmacher, who read a draft of the report. Also, he said, the report counts only premature births, not stillbirths. In this country, a fetus in danger is delivered early, which raises the preterm birth count, while in much of Africa, the infant would die, and not be counted.
Preemies are, of course, much more likely to die in poor countries.
In the United States, an infant born before 28 weeks has a 90 percent chance of surviving, though often with disabilities, while in most of Africa such a child has a 90 percent chance of dying, according to the report.
(The report defined full-term as 39 weeks; other authorities use 37 to 40 weeks.)
Complications of premature birth are, after pneumonia, the second-highest cause of death in infants, the report said. Over 80 percent of the 1.1 million babies who die of birth complications every year are in Africa or South Asia.
Many could be easily and cheaply saved, the report said.
Steroid injections for mothers in early labor, which help develop immature fetal lungs and cost only $1, could save almost 400,000 a year.
Teaching “kangaroo care” — wrapping the baby against the mother’s chest to keep it warm and promote breast-feeding, could save another 450,000.
Wiping first-aid cream on the stump of the umbilical cord and having antibiotics on hand to fight pneumonia would save more lives, the report said.
The report took years to produce because there is no global database, Dr. Lawn said, and many countries measure pregnancies differently — by baby weight or by mother’s last period, among other methods.
The spread of ultrasound machines has made measurement more accurate, she said.
Because the triggers for premature labor are not fully understood, the poor performance by the United States is partly a mystery, Dr. Guttmacher said.
“This underscores the need for more research,” he said.
In his study of 2,100 Mexican-Americans and immigrants from Mexico, Dr. Radek K. Bukowski, an expert on preterm birth at the University of Texas Medical Branch in Galveston, found that the longer a woman lived in this country, the greater her chances of giving birth prematurely grew. Recent immigrants had a 4 percent risk, those living here less than a decade were at 7 percent, and citizens were at 10 percent.
Even after controlling for risk factors like age, poverty, smoking, obesity and diabetes, “we really don’t have an explanation for what’s behind it,” he said. “But whatever it is, it’s not genetic. It’s something they acquire here.”
And Dr. Gordon C. S. Smith, an expert in the same field at the University of Cambridge, noted that his native Scotland had many of the same risk factors as the United States — teenage pregnancies, poverty, obesity and older mothers — and yet has much lower rates.
“If somebody had a simple explanation of why the U.K. and Europe do much better, I wouldn’t believe them,” he said. “The reality is, for most preterm births, we just don’t understand the cause.”
The report singled out some countries for bringing down their rates of premature birth. Croatia, Ecuador and Estonia improved rapidly, Dr. Lawn said. Croatia was easy to explain: a war ended. The other two countries became wealthier and applied some of that wealth to saving babies’ lives.
The report also praised Turkey and Sri Lanka for cutting their rates rapidly. Sri Lanka made sure pregnant women were visited frequently by trained midwives. Turkey even paid rural women to come to hospitals to give birth and created “maternity homes” where they waited out their pregnancies’ final days.