Infant mortality is on the decline in the United States, a recent report  from the Centers for Disease Control and Prevention (CDC) reveals.
Over the past decade, infant mortality has dropped nationwide by 15%. While infant mortality in the U.S. stood at 6.86 infant deaths for every 1,000 live births in 2005, by 2014, that rate had declined to 5.82 deaths per 1,000 births. The infant mortality rate (IMR) in the U.S. has decreased every year since 2007.
According to the CDC’s National Center for Health Statistics (NCHS),  infant mortality declined significantly in 33 states. Colorado, South Carolina, and Connecticut made the greatest progress proportionally, each seeing infant mortality plummet by more than 20%. The District of Columbia, however, saw the most precipitous decline with infant mortality falling by 43%.
A steady decrease in the mortality rate from the three leading causes of infant death—congenital abnormalities, short gestation/low birthweight, and sudden infant death syndrome (SIDS)—helped, in part, to drive the trend. Out of the top five leading causes of infant mortality, the proportion of deaths due to SIDS declined most, proportionally, falling by 29% since 2005.
Despite recent gains, however, infant mortality in the United States still remains higher than in Europe and other developed countries. In 2014, the U.S. ranked 30th out of 35 member states of the Organization for Economic Co-operation and Development (OECD). In fact, each one of the top ten ranked OECD countries had infant mortality rates less than half of that of the U.S.
In 1960, the U.S. ranked 11th among current OECD member states. Over the intervening decades, however, the U.S. gradually slipped in ranking as infant mortality in other emerging economies countries declined faster and eventually outpaced the U.S.
While infant mortality has consistently declined in the U.S. since the early part of the 20th century, progress stagnated at the turn of the 21st century. Between 2000-2005, there was no significant decrease in the infant mortality rate. 
The reasons why the U.S. continues to lag behind other developed countries on infant mortality are multifaceted and not entirely understood.
One contributing factor may be due to better reporting of very early preterm births in the U.S. compared to other countries. While most countries, like the U.S., report all live births regardless of gestational age, some European countries do not count births prior to 22 weeks or infants that weigh less than 500 grams.
But even if the playing field were leveled, so to speak, to include only births after 24 weeks gestation, the U.S. would still be far behind many of its European peers. A NCHS study  found that excluding births after 24 weeks gestation in 2010 would have reduced IMR in the U.S. by approximately 31%. Even so, this lower rate was still twice as high as the IMR after 24 weeks in both Sweden and Finland.
According to the NCHS, infant mortality in the U.S. remains particularly high due to a higher percentage of preterm births (births prior to 37 weeks) relative to other developed countries.
Preterm births are not the only contributing factor, however. The NCHS found that in comparison to Sweden, the U.S.’s higher mortality after 37 weeks gestation in 2010 contributed more to the higher U.S. IMR than preterm births.
Certain underlying health conditions may also be to blame. The U.S. has the highest level of obesity of any OECD country.
Several demographic factors such as education and marital status may also play a role in affecting infant mortality.
Women with more education are less likely to experience infant demise. In 2011, the infant mortality rate for women without a high school diploma was 7.54 deaths per 1,000 live births. But for women with a bachelor’s or postgraduate degree, the infant mortality was nearly half that rate at 3.63 per 1,000 live births.
Similarly, infant mortality is notably higher among unwed mothers than among married women. In 2014, infant mortality for married women was 4.47 deaths per 1,000 live births, but among unwed mothers, the rate was much higher at 7.83 per 1,000 births. 
Over the past several decades, the percentage of births to unmarried women has increased tremendously in both the United States and other developed countries. Although this trend in the U.S. appears to have leveled off since 2008, the high percentage of women bearing children outside of the context of a marital union could unnecessarily hinder progress in reducing IMR.
Many studies have shown marriage to be a protective factor against infant mortality. Marriage, as an institution, appears to provide a bundle of benefits for both women and their children, particularly in social contexts where marriage is a social norm.
Even in contexts where marriage as a societal norm has been sufficiently weakened and secularized, marriage is protective against risk factors for infant demise. A hospital-based study in Finland (during a time when unwed childbearing averaged a little below its prevalence in the U.S. today) found that single and cohabiting women were significantly more likely than their married peers to have a preterm delivery (unmarried ORadj = 1.15; 95% CI: 1.03–1.28) and low birth infant birth weight (unmarried ORadj = 1.17; 95% CI: 1.03–1.32).  Another study found that, even in countries where out-of-wedlock childbearing was fairly common, unmarried women were significantly more likely to have an early preterm birth less than 33 weeks gestation. 
Unmarried women in the U.S. are also significantly less likely to quit smoking during pregnancy than married women,  which could contribute to lower preterm birth and lower SIDS among married women. Unmarried women are also far more likely to smoke prior to pregnancy and resume smoking after delivery.
In the U.S., alarming racial disparities for infant mortality continue to persist. While infant mortality among Asians & Pacific Islanders was 3.86 per 1,000 live birth in 2014, IMR among non-Hispanic blacks was more than twice as high at 10.93. 
Several states have made reducing infant mortality a public health priority. New Jersey, Ohio, and Alabama have recently offered to give mothers with free baby boxes , equipped with foam mattresses and tight fitting sheets to prevent SIDS by providing a safe sleeping environment for newborns.
In 2011, South Carolina forged a public-private alliance between the state’s Medicaid program and BlueCross BlueShield, the state’s largest private insurer, to disincentivize early elective induced deliveries. And it seems to have worked. While South Carolina had the 12th highest IMR nationwide for infants born at 37-39 weeks gestation, by 2014, the state had cut down on its 37-39 week IMR by a whopping 30.5%, the fastest decline of any state nationwide.
The initiative not only protected infant health by delaying the onset of labor, it also saved the state of South Carolina an estimated $6 million in Medicaid spending in the first quarter of 2013.
Overall, the decline in U.S. infant mortality rates in recent years is welcome news. But more still can, and needs, to be done to reduce the number of infant deaths yet further.
 Mathews TJ, Driscoll AK. Trends in infant mortality in the United States, 2005–2014. NCHS data brief; no 279. Hyattsville: National Center for Health Statistics, 2017.
 MacDorman MF, Mathews TJ. Recent trends in infant mortality in the United States. NCHS data brief; no 9. Hyattsville: National Center for Health Statistics, 2008.
 MacDorman MF, Mathews TJ, Mohangoo AD, Zeitlin J. International comparisons of infant mortality and related factors: United States and Europe, 2010. National vital statistics reports; vol 63, no 5. Hyattsville: National Center for Health Statistics, 2014.
 Centers for Disease Control and Prevention, National Center for Health Statistics. 2011 Linked Birth/Infant Death File. Analyzed by the Maternal and Child Health Bureau. Accessed at https://mchb.hrsa.gov/chusa14/health-status-behaviors/infants/infant-mortality.html
 Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), Division of Vital Statistics. Linked Birth/Infant Death Records, 2014. CDC WONDER online database. [cited 2017 Mar 28]. Accessed at http://wonder.cdc.gov/lbd-current.html
 Raatikainen K, Heiskanen N, Heinonen S. Marriage still protect pregnancy. BJOG 2005; 112: 1411-1416.
 Zeitlin JA, Saurel-Cubizolles MJ, Ancel PY, EUROPOP Group. Marital status, cohabitation, and risk of preterm birth in Europe: where births outside marriage are common and uncommon. Paediatr Perinat Epidemiol 2002; 16(2): 124-30.
 Colman GJ, Joyce T. Trends in smoking before, during, and after pregnancy in ten states. Am J Prev Med 2003; 24(1): 29-35.
 Mathews (2017).