Carrie K. Shapiro-Mendoza, PhD1; Wanda D. Barfield, MD1; Zsakeba Henderson, MD1; Arthur James, MD2; Jennifer L. Howse, PhD3; John Iskander, MD4; Phoebe G. Thorpe, MD4 (View author affiliations)
Preterm birth (delivery before 37 weeks and 0/7 days of gestation) is a leading cause of infant morbidity and mortality in the United States. In 2013, 11.4% of the nearly 4 million U.S. live births were preterm; however, 36% of the 8,470 infant deaths were attributed to preterm birth (1). Infants born at earlier gestational ages, especially <32 0/7 weeks, have the highest mortality ( Figure) and morbidity rates. Morbidity associated with preterm birth includes respiratory distress syndrome, necrotizing enterocolitis, and intraventricular hemorrhage; longer-term consequences include developmental delay and decreased school performance. Risk factors for preterm delivery include social, behavioral, clinical, and biologic characteristics ( Box). Despite advances in medical care, racial and ethnic disparities associated with preterm birth persist. Reducing preterm birth, a national public health priority (2), can be accomplished by implementing and monitoring strategies that target modifiable risk factors and populations at highest risk, and by providing improved quality and access to preconception, prenatal, and interconception care through implementation of strategies with potentially high impact.
Most preterm births are spontaneous and can occur with intact membranes (40%–45% of preterm births) or after preterm premature rupture of membranes (25%–30% of preterm births) (3). The etiology of preterm labor is poorly understood; prevailing theories include infectious and inflammatory processes. Intrauterine infection and inflammation might account for up to 40% of preterm births, but in many instances, the cause might be subclinical and difficult to detect (3,4). Maternal or fetal complications can often result in preterm birth because of medically indicated induction of labor or cesarean delivery (30%–35% of preterm births) (3). Growing awareness of the complications of prematurity has prompted careful evaluation of the indications for and timing of delivery (5).
For more accurate estimates of the preterm birth rate, CDC’s National Center for Health Statistics transitioned from using the date of last normal menstrual period to the obstetric estimate of gestation at delivery, starting with 2014 births and revising data back to 2007 (6).* Based on the historical last normal menstrual period measure, the U.S. preterm birth rate increased 21%, from 10.6% in 1990 to 12.8% in 2006 (7). Since 2007, the first year that data using the obstetric estimate of gestation at delivery were available, the overall rate declined, from 10.4% in 2007 to 9.6% in 2014. However, declines have been disproportionate across racial and ethnic groups (6). In 2014, non-Hispanic black (black) women had the highest preterm birth rate (13.2%), followed by American Indians or Alaska Natives (AI/AN) (10.2%), Hispanics (9.4%), non-Hispanic whites (whites) (8.9%), and Asian/Pacific Islanders (API) (8.5%). Compared with the preterm birth rate among whites, the rates of preterm birth among blacks and AI/AN were 1.5 and 1.1, respectively (6).
Declines in infant mortality (53%) since the 1980s have been largely attributed to increasing preterm survival, owing to improvements in neonatal intensive care and treatments for lung immaturity. Infant mortality rates (deaths in children aged <12 months per 1,000 live births) declined from 12.6 in 1980 (8) to 5.96 in 2013 (1).† Despite these declines, racial and ethnic disparities persist. In 2013, the infant mortality rate among black infants (11.2) was 2.2 times higher than that among white infants (5.1). Rates of preterm-related infant mortality§ (per 1,000 live births) provide further evidence of racial and ethnic disparities and highlight the importance of reducing preterm births. Black women have the highest rates of preterm-related infant mortality (4.9), followed by AI/AN women (2.0), Hispanic women (1.8), white women (1.6), and API women (1.5) (1).
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Shapiro-Mendoza CK, Barfield WD, Henderson Z, et al. CDC Grand Rounds: Public Health Strategies to Prevent Preterm Birth. MMWR Morb Mortal Wkly Rep 2016;65:826–830. DOI: http://dx.doi.org/10.15585/mmwr.mm6532a4
