Social and Economic Contributors to Neonatal Outcome in the United States

Infant Mortality

While the United States had a steady decline in infant mortality over the past decade, declining 15% from 6.86 deaths per 1000 live births in 2005 to 5.82 per 1000 in 2014, this rate is still almost twice that of other comparable countries in the world. Data comparing infant mortality from 2010 indicated that the United States had 2 to 3 times the infant mortality rate of countries such as Germany and Sweden, in spite of significantly larger health care expenditures in the United States per capita compared to these other countries. Multiple studies have attempted to delineate the factors unique to the United States that might explain this discrepancy. One possible explanation is the high number of infants born and resuscitated at 22 and 23 weeks’ gestation in the United States compared to many countries in Europe. However, excluding these infants still indicates a US infant mortality rate twice that of these countries. Addressing prematurity is a significant health and financial priority. Although only 9.1% of birth hospitalizations were among preterm or low birth weight infants, these births accounted for 43.4% of total costs of neonatal care.

Prematurity (infants born at less than 37 weeks) in the United States has a major impact on high infant mortality rates. Studies show that the United States has rates of prematurity up to two times that of other developed countries. Clearly, this is a significant contributor to the high infant mortality seen in the United States. During the 1990s and early 2000s, the US preterm birth rate steadily increased from 10.6% in 1990 to 12.8% in 2006. The United States overall saw a steady decrease in the prematurity rate over the past decade, with a decrease from 10.44% in all births in 2007 to 9.57% in 2014. Disturbingly, this trend in the prematurity rate has reversed in recent years with a small but significant increase to 9.63% in 2015 and 9.84% in 2016, primarily due to an increase in late preterm births. It is unclear how this will impact the recent improvements in US infant mortality.

Addressing the causes of prematurity is critical to reducing the US infant mortality rate. However, a higher rate of prematurity alone does not explain the higher US infant mortality rate, as the gestational-age-specific infant mortality rates are also increased above other countries at gestational ages 32 weeks and above, the category with the highest number of preterm births.

It is now well established that major contributors to infant mortality rates in the United States are the significant health disparities. The major health disparity is related to racial and ethnic differences of perinatal health outcomes in all states in the United States, with a wide variation state to state.

Epidemiologic studies have shown that non-Hispanic black infants have an infant mortality rate over two times that of non-Hispanic white infants (10.93 deaths per 1000 live births in 2014 vs. 4.89 per 1000 live births) ( Fig. 9.1 ). American Indian or Alaskan Native infants also exhibit substantially higher infant mortality rates than non-Hispanic whites. Interestingly, Asian or Pacific Islander infants have consistently exhibited the lowest neonatal and infant mortality rates for many years, while Hispanic infant mortality rates track close to non-Hispanic white infant mortality rates in spite of economic disadvantages and poor health care access.

From 2005 to 2014, infant mortality rates overall and for each race or ethnic group had decreased each year. However, in recent years, this decline has plateaued. It appeared that the United States was making great strides in reducing the discrepancies in infant mortality rates related to race with a 16% decline from 2005 to 2011 seen in non-Hispanic black rates compared to the overall US decline of 12% during those years. A closer look at recent US infant mortality data shows disturbingly that from 2013 to 2014, only non-Hispanic whites had a significant 3% decrease; other groups did not show a statistically significant improvement. In fact, the 2015 data indicate that for non-Hispanic black infants the infant mortality rate actually increased from a low of 11.4 per 1000 in 2014 to 11.7 per 1000 in 2015. This is in sharp contrast to the infant mortality rate of 4.8 per 1000 in non-Hispanic white infants in 2015. Thus, it appears that in the United States, these disparities by race are worsening. In addition, there are significant differences in infant mortality by state, with the southern states having the highest infant mortality. These are also the states with the highest percentage of non-Hispanic black women in their population ( Fig. 9.2 ).

Similar to significant disparities seen in infant mortality, the incidence of prematurity varies greatly by race and ethnicity, with the provisional 2016 percent of births under 32 weeks for non-Hispanic blacks at almost three times that of non-Hispanic whites (3.16% vs. 1.26%) ( Table 9.1 ). Disturbingly, US prematurity rates for less than 37 weeks gestation are slightly increased in 2016 compared to 2015 and 2014 for the United States.

The five leading causes of infant mortality in the United States are congenital malformations, short gestation and low birth weight, SIDS (sudden infant death syndrome) or SUID (sudden unexpected infant death), maternal complications, and unintentional injuries. Data show that these causes of death vary by racial and ethnic group. For example, death due to low birth weight/preterm-related causes is over 3-4 times higher in non-Hispanic blacks compared to non-Hispanic whites. In contrast, the high infant mortality seen in Native Americans and Alaska Natives occurs in those babies born at much higher birth weights and would appear to be less impacted by prematurity. There are also differences in mortality noted within certain ethnic groups. For Puerto Rican infants, the rate of infant mortality due to preterm causes is almost twofold that of non-Hispanic whites and is the highest among all of the Hispanic subgroups. This could reflect the longer-term presence of the Puerto Rican population in the United States compared to more recent Hispanic immigrants and the cumulative toxic effect in the United States of low socioeconomic states (SES) over time on adverse pregnancy outcomes.

Congenital anomalies and subsequent infant mortality are also impacted by health disparities. Bassil et al. found that socioeconomic inequities lead to a significant increase in major congenital anomalies in babies born to mothers in areas of highest deprivation. Further analysis revealed that there were higher odds of chromosomal and multiple systems anomalies in the highest deprivation areas. These findings could be explained by higher exposure to teratogens or to poor health of these disadvantaged mothers.

Post-neonatal mortality also exhibits racial and ethnic disparities as seen in SIDS/SUID, a leading and increasing cause of infant mortality. The vast majority of infant autopsies identifying the cause of death due to SIDS or SUID are from infants born at 37-42 weeks. For American Indian or Alaska Natives, the largest difference in mortality outcomes when compared to non-Hispanic whites is the two- to threefold increase in deaths due to SUID (American Indian: 177 per 100,000 live births, non-Hispanic white: 84.5 per 100,000 live births). Non-Hispanic blacks also have an extremely high rate of mortality from SUID (172.4 per 100,000 live births), only slightly lower than the rate for Native American infants. The lowest rate of SUID is seen in Hispanic and Asian/Pacific Islander infants (Hispanic: 49.3 per 100,000 live births, Asian/Pacific Islanders: 28.3 per 100,000 live births), even lower than the non-Hispanic white rate. A significant impact on SUID is decreasing gestational age at birth, with infants born at 24-27 weeks having a 3.5–5-fold increase in the rate of SIDS compared to term infants. Again, racial disparities are seen, with an SUID rate in non-Hispanic blacks at less than 28 weeks of 382.3 per 100,000 live births compared to the lowest group, Asian/Pacific Islanders: 126.6 per 100,000 live births at less than 28 weeks. Given that the highest rate of prematurity is seen in non-Hispanic blacks, this contribution to SIDS/SUID also negatively impacts this population and infant mortality. In addition, overall, the SUID group had twice the percentage of African American mothers and was independently associated with this adverse outcome. There are racial and ethnic differences in positioning of babies for sleep, with Hispanic and non-Hispanic black infants and infants in southern states being placed supine much less often than non-Hispanic white infants. Premature infants are also positioned more often in the prone position as well. Alarmingly, many states have reported a recent increase in deaths due to SIDS/SUID in the non-Hispanic black population for unclear reasons. Again, it is unclear what impact genetic versus cultural factors may play in this adverse outcome. This would imply that both genetic and cultural aspects of race and ethnicity contribute to differing SIDS/SUID outcomes as well as lower SES.

Mirroring the infant mortality rates, fetal deaths and perinatal mortality rates show wide variation by race and ethnicity. Non-Hispanic black fetal mortality rates are twice as high as non-Hispanic white rates, with American Indian or Alaska Native fetal and perinatal mortality rates intermediate. Poorer maternal health and decreased access to prenatal care may have an impact on this.