Preterm Birth

More than a half million babies in the United States—that's 1 of 8—are born premature each year. Learn more about prematurity.

Preterm birth is the birth of an infant at least three weeks before the due date (less than 37 weeks gestation). The risks associated with being born preterm are greater at earlier gestational ages compared to later gestational ages. Death and disability occur more often among these very preterm infants compared to moderately preterm infants. Unfortunately, all preterm infants are at greater risk of death and disability than full-term infants. Infants born preterm are at greater risk for death in the first few days of life, as well as other adverse health outcomes including visual and hearing impairments, intellectual and learning disabilities, and behavioral and emotional problems throughout life. Preterm births also cause substantial emotional and economic burdens for families. Most preterm births occur because labor begins too early or there is a rupture of the fetal membranes before term. In some cases, infants are delivered preterm because the risks to the mother or baby to continue the pregnancy exceed the risks associated with being born early.
Multiple-infant births are associated with more problems for both mothers and infants, including higher rates of caesarean section, prematurity, low birth weight, and infant disability or death. The risk of preterm delivery and of low or very low birth weight is increased using Assisted Reproductive Technology (ART) to conceive a baby. This is largely because of the higher risk of multiple pregnancy. Data indicate that the risk for preterm birth is higher among infants conceived through ART than for infants in the general population.
Preterm birth also occurs more often among some racial and ethnic groups. For example, African American women have a much greater risk of delivering a preterm baby than white women. The most important risk factor for delivering preterm is having delivered preterm in a previous pregnancy. Because of this, women who have had a preterm birth and are thinking about another pregnancy should discuss this with their health care provider. There are no perfect methods for preventing preterm birth. However, clinical research continues to identify ways to help women prevent the first or subsequent episode of preterm delivery. For example, a compounded product with progesterone (17-hydroxyprogesterone caproate or 17P) may hold promise for women who have experienced a premature birth in the past.

The U. S. Food and Drug Administration (FDA) recently approved hydroxyprogesterone caproate (Makena™) to reduce the risk of preterm delivery before 37 weeks of pregnancy, in pregnant women with a history of at least one spontaneous preterm birth. The drug must be injected for use. It is not intended for use in women with a multiple pregnancy, such as a twin pregnancy, or other risk factors for preterm birth. For more information on FDA’s approval, see their press announcement

. Information on this and other drugs, including whether they are safe for use during pregnancy, can be obtained from http://druginfo.nlm.nih.gov

The reasons for preterm births remain unclear. CDC scientists are collaborating with many partners, including states, university researchers, and partners in health care to understand why preterm births occur and what can be done to help prevent them. Learn more about CDC preterm birth research activities.
Premature baby, foot in fathers hand.

Although approximately 1 out every 8 pregnancies in the United States results in preterm birth, a recent report from CDC’s National Center for Health Statistics shows a small but encouraging decline in the preterm birth rate. While this is encouraging, levels remain higher than at any point in the 1980s and 1990s. Most of this increase has been among late preterm births (34–36 weeks).
Ongoing reviews of infant death data by CDC researchers continue to demonstrate that preterm-related deaths account for more than 1/3 of all deaths during the first year of life, and more infants die from preterm causes than from any other cause.

2006 Preterm-Related Infant Mortality Rates (Per 1000 Live Births) and Percent of Total Infant Deaths that are Preterm-Related

All races or origin	2.42	36.1
non-Hispanic white	1.79	32.1
non-Hispanic black	6.01	45.0
American Indian or Alaska Native	2.10	25.3
Asian or Pacific Islander	1.49	32.6
Mexican	1.71	32.0
Puerto Rican	3.30	41.2
Central and South American	1.52	33.7

Source: Infant Mortality Statistics from the 2006 Period Linked Birth/Infant Death Data Set

NVSR 2010;58(17) [ PDF - 744KB].
Preterm-related infant mortality rates vary by maternal race and ethnicity. In 2006, these rates were 3.4 times higher for non-Hispanic black (6.01 per 1,000 live births) than for non-Hispanic white (1.79) mothers.