Preterm Birth - Epidemiology

Epidemiology

In Europe and many developed countries the preterm birth rate is generally 5–9%, and in the USA it has even risen to 12–13% in the last decades. Three obstetric events precede preterm birth: spontaneous preterm births are the 40–45% preterm births that follow preterm labor and the 25–30% preterm births after premature rupture of membranes. The remainder (30–35%) are preterm births that are induced for obstetrical reasons; obstetricians may have to deliver the baby preterm because of a deteriorating intrauterine environment (i.e. infection, intrauterine growth retardation) or significant endangerment of the maternal health (i.e. preeclampsia, cancer). By gestational age, 5% of preterm births occur at less than 28 weeks (extreme prematurity), 15% at 28–31 weeks (severe prematurity), 20% at 32–33 weeks (moderate prematurity), and 60–70% at 34–36 weeks (late preterm).

As weight is easier to determine than gestational age, the World Health Organization tracks rates of low birth weight (< 2,500 grams), which occurred in 16.5 percent of births in less developed regions in 2000. It is estimated that one-third of these low birth weight deliveries are due to preterm delivery. Weight generally correlates to gestational age, however, infants may be underweight for other reasons than a preterm delivery. Neonates of low birth weight (LBW) have a birth weight of less than 2500 g (5 lb 8 oz) and are mostly but not exclusively preterm babies as they also include small for gestational age (SGA) babies. Weight-based classification further recognizes Very Low Birth Weight (VLBW) which is less than 1500 g, and Extremely Low Birth Weight (ELBW) which is less than 1000 g. Almost all neonates in these latter two groups are born preterm.

Preterm birth is a significant cost factor in healthcare, not even considering the expenses of long-term care for individuals with disabilities due to preterm birth. A 2003 study in the US determined neonatal costs to be $224,400 for a newborn at 500–700 g versus $1,000 at over 3,000 g. The costs increase exponentially with decreasing gestational age and weight. The 2007 Institute of Medicine report Preterm Birth found that the 550,000 preemies born each year in the U.S. run up about $26 billion in annual costs, mostly related to care in NICUs, but the real tab may top $50 billion.