A study of the connection between preterm birth and infant mortality examined 27,970 records from 2002 linking U.S. infant death and birth certificates and found that preterm birth was the primary cause of infant death,⁷ not the secondary cause (after congenital anomalies) as previously reported.¹ Preterm infants made up 68.6% of all U.S. infants who died in 2005.⁸ Of the 4 million infants world-wide who die each year within the first four weeks of life, 1.1 million (28%) die because they’re premature.⁹

Recent increases in multiple births have contributed to the rise in the incidence of preterm births, but premature births have also increased among singleton deliveries. ^{5, 10} The greatest increase in preterm births has occurred in “late-preterm” infants—those between 34 and 36 weeks’ gestation. ¹¹ In fact, the gestational age of spontaneous singleton births in the United States is now significantly younger: in 1992 most infants were born at 40 weeks’ gestation; most were born at 39 weeks’ gestation 10 years later.¹² Medical intervention has been implicated in the shift toward earlier gestational age at birth. In 1992, 29% of births required a cesarean delivery or induction of labor, but by 2005, 30.3% of infants were being delivered by cesarean section, whether medically necessary or elective, and 22.3% of women giving birth had their labor induced, more than twice the 1990 rate of 9.5%.⁵ In 2005 late-preterm births accounted for 71.6% of all preterm births in the United States.⁵ And late-preterm infants have a mortality rate that’s three times that of full-term infants.¹³

Advances in neonatal care have improved preterm infant survival, particularly among extremely low-birth-weight infants.³ But among infant survivors of preterm birth and extremely low birth weight from 2000 to 2002, 23% suffered a major neurologic disability. ³ A 2000 study by St. John and colleagues estimated that for all neonates born between 1989 and 1992 in the United States, initial postdelivery, in-hospital care alone cost $10 billion annually.¹⁴ Infants born full-term at 37 weeks’ gestation or later were responsible for 42.7% of those costs, and infants born at 32 weeks’ gestation or earlier for 11.9%, but the authors noted that the latter percentage was low only because few infants were born so early. A 2005 study in AJN showed that mean hospital charges for infants born in 2001 at 26 to 28 weeks’ gestation were $239,749 compared with only $4,788 for infants born at 37 weeks’ gestation or later.⁴ Delaying the birth of an infant from less than 29 weeks’ gestation to full-term is estimated to save at least $122,000 per case.¹⁵

In response to the increased incidence of preterm births in the United States, the March of Dimes has released its first annual Premature Birth Report Card, in which the organization grades each state according to how its rates of preterm births compare to the goals of the Healthy People 2010 initiative. In its first report card issued last November, the nation as a whole received a D; Vermont received the highest grade, a B; and 18 states received an F. The report card is the organization’s attempt to raise public awareness about this issue. (For more information, go to www.marchofdimes.com.) Although the Healthy People 2010 initiative recommends reducing preterm births to 7.6% of all births,¹⁶ that goal can be achieved only with greater understanding of the many factors involved.

Both full-term labor and preterm labor involve activation of the decidua (membranes lining the uterus), cervical ripening, and uterine contractions. In full-term labor this process is physiologic; in preterm labor and birth it’s pathologic.²⁰ Romero and colleagues have hypothesized a preterm parturition syndrome that includes the following²⁰: