Race and Ethnic Disparities in Fetal Mortality, Preterm Birth, and Infant Mortality in the United States: An Overview

Race and Ethnic Disparities in Fetal Mortality, Preterm Birth, and Infant Mortality in the United States: An Overview Marian F. MacDorman, PhD Infant mortality, fetal mortality, and preterm birth all represent important health challenges that have shown little recent improvement. The rate of decrease in both fetal and infant mortality has slowed in recent years, with little decrease since 2000 for infant mortality, and no significant decrease from 2003 to 2005 for fetal mortality. The percentage of preterm births increased by 36% from 1984 to 2006, and then decreased by 4% from 2006 to 2008. There are substantial race and ethnic disparities in fetal and infant mortality and preterm birth, with non-Hispanic black women at greatest risk of unfavorable birth outcomes, followed by American Indian and Puerto Rican women. Infant mortality, fetal mortality, and preterm birth are multifactorial and interrelated problems with similarities in etiology, risk factors and disease pathways. Preterm birth prevention is critical to lowering the infant mortality rate, and to reducing race and ethnic disparities in infant mortality. Semin Perinatol 35:200-208 Published by Elsevier Inc. KEYWORDS infant mortality, fetal mortality, preterm birth, race and ethnic disparities, vital statistics

F

etal mortality, preterm birth, and infant mortality all represent important public health challenges that have shown little recent improvement, despite programmatic efforts at the federal, state, and local levels. The purpose of this article is to provide an overview of trends and patterns in fetal mortality, preterm birth, and infant mortality, including race and ethnic disparities. Most of the data in this article are from birth certificates, death certificates, and reports of fetal death filed in state vital statistics offices and transmitted to the National Center for Health Statistics (NCHS). For each event (fetal death, preterm birth, infant mortality) the latest data available at the time of manuscript preparation were used.

Fetal Mortality Fetal mortality is a major, but often overlooked, public health problem. There were an estimated 6.4 million pregnancies in the United States in 2005, including 4.1 million live births, 1.2 million induced abortions, and 1.1 million fetal deaths at

Reproductive Statistics Branch, Division of Vital Statistics, NCHS, Hyattsville, MD. Address reprint requests to Marian F. MacDorman, PhD, Reproductive Statistics Branch, Division of Vital Statistics, NCHS, 3311 Toledo Rd, Rm 7318, Hyattsville, MD 20782. E-mail: [email protected]

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0146-0005/11/$-see front matter Published by Elsevier Inc. doi:10.1053/j.semperi.2011.02.017

any gestational age, of which the vast majority occur early in pregnancy.1 NCHS recommends that all fetal deaths weighing 350 g or more, or of 20 weeks of gestation or more, be reported through the National Vital Statistics System, and most U.S. states report fetal death data at this level but with some variation in data completeness and quality.2 Even if you only consider fetal deaths at 20 weeks of gestation or more, there are nearly as many fetal deaths as infant deaths in the United States each year. In 2005, 25,894 fetal deaths of 20 weeks or more were reported, compared with 28,384 infant deaths.3 In 2005, the U.S. fetal mortality rate was 6.22 fetal deaths of 20 weeks of gestation or more per 1000 live births and fetal deaths, compared with an infant mortality rate of 6.86.2,3 Fetal mortality decreased more slowly than infant mortality during the 1990s (Fig. 1). From 1990 to 2000, the U.S. fetal mortality rate decreased by an average of 1.4% per year, whereas the infant mortality rate decreased by 2.8% per year. The infant mortality rate has shown little or no decline since 2000, and there has also been a slowing in fetal mortality decline, with no statistically significant decline from 2003 to 2005.2-4 All decreases in the fetal mortality rate since 1990 have been among late fetal deaths (28 weeks of gestation or more). There has been little or no change in the fetal mortality rate at 20-27 weeks of gestation since 1990.2

Race and ethnic disparities in infants in the U.S.

201

Figure 1 Fetal and infant mortality rates and percentage of preterm births: United States, 1990-2008.

Risk Factors for Fetal Mortality Fetal mortality rates vary considerably by race and Hispanic origin of the mother (Table 1). The fetal mortality rate for non-Hispanic black women was 11.13, which was 2.3 times the rate for non-Hispanic white women at 4.79. Approximately two-thirds of the difference was attributable to greater non-Hispanic black fetal mortality at 20-27 weeks of gestation. The fetal mortality rate for American Indian women was 29% greater, and the rate for Puerto Rican women was 27% greater than for non-Hispanic white women. The risk of fetal mortality is much greater in multiple than in single pregnancies. In 2005, the fetal mortality rate for twins was 16.08 fetal deaths per 1000 live births and fetal Table 1 Fetal and Infant Mortality Rates and Percentage of Preterm Births by Race and Ethnicity, United States, Most Recent Available Data Infant

Fetal

Percentage

Mortality Mortality of Preterm

Total Non-Hispanic white Non-Hispanic black American Indian or Alaska native Asian or Pacific Islander Hispanic total‡ Mexican Puerto Rican Cuban Central and South American

Rate, 2006*

Rate, 2005†

Births, 2007

6.68 5.58 13.35 8.28

6.22 4.79 11.13 6.17

12.7 11.5 18.3 13.9

4.55

4.78

10.9

5.41 5.34 8.01 5.08 4.52

5.44 5.24 6.09 4.15 4.50

12.3 11.9 14.5 13.4 12.1

*Rate per 1000 live births in specified group. †Rate per 1000 live births and fetal deaths in specified group. ‡Includes persons of other and unknown Hispanic origin not shown separately.

deaths, or 2.7 times the rate for singletons (5.85). The fetal mortality rate for triplet or higher-order pregnancies was 27.18, or 5 times the rate for singletons. Because of their greater risk of fetal death, multiple pregnancies comprise 3% of live births but 9% of fetal deaths in the United States each year.2,3 When examined by maternal age, the risk of fetal death was lowest among women 25-29 years and greater for teenagers and for older mothers. The fetal mortality rate for women ⬍15 years old was 12.20, more than twice the rate for women aged 25-29 (5.47). The rate for teenagers 15-19 years was 7.54, 38% greater than for women 25-29 years. The greater risk for teenagers may be related to less favorable socioeconomic and behavioral conditions among pregnant teenagers, although biological immaturity may also play a role, particularly for the youngest teens.5 At the opposite end of the age spectrum, fetal mortality rates also increased sharply for women 35 and older. For women 45 years and older, the fetal mortality rate in 2005 was 15.51, 2.8 times the rate for 25-29 year olds. Maternal age older than 35 years appears to be an independent risk factor for fetal death, even after adjusting for medical conditions that are more common among older women, such as hypertension, diabetes, and multiple gestation.6-8 However, the magnitude of the elevated risk varies somewhat by race.2,9 Fetal mortality rates also vary considerably by the number of previous pregnancies. The fetal mortality rate for women with 1 previous pregnancy was 4.87, compared with a rate of 5.88 for women with no prior pregnancy. Fetal mortality rates increase for women with 2 or more previous pregnancies, and the fetal mortality rate for women with 4 or more prior pregnancies was 11.42, more than twice the rate of 4.87 for women with 1 previous pregnancy.3 Other risk factors for fetal mortality include maternal smoking, maternal obesity, severe or uncontrolled hypertension or diabetes, congenital anomalies, infections, placental and cord problems, intrauterine growth retardation, previous perinatal death, and previous cesarean section.10-16

M.F. MacDorman

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Figure 2 Prospective fetal mortality rate by single weeks of gestation: United States, 2005.

Prospective Fetal Mortality Rate The traditional way to compute fetal mortality rates by gestational age is per 1000 live births and fetal deaths at the specific gestational age. However, a more appropriate indication of the population at risk of fetal death may actually be all the women who are still pregnant at that gestational age. Thus, the prospective fetal mortality rate is the number of fetal deaths at a given gestational age, per 1000 live births and fetal deaths at that gestational age or greater.2 Using this measure, we see 2 distinct peaks in fetal mortality risk: early fetal mortality at ⬍23 weeks of gestation, and late fetal mortality at 40 weeks of gestation or more (Fig. 2). These 2 peaks suggest etiologic differences. Early fetal mortality may be more related to congenital anomalies, infections, uteroplacental insufficiency, and underlying maternal medical conditions.17 Fetal mortality at 40 weeks or more may include these factors, but may also relate to problems that manifest around the time of delivery, such as placental and cord problems, or other problems in the labor and delivery process. However, research on late fetal deaths has found that a substantial number are of unknown cause.7,17-19

Preterm Birth Preterm birth is perhaps the most important factor influencing an infant’s subsequent health and survival. Compared with term infants (37-41 weeks of gestation), preterm infants (⬍37 weeks of gestation) have a much greater risk of death and a wide variety of health and developmental problems, including long-term cognitive, behavioral, social, emotional, and neurodevelopmental difficulties.20-22 The percentage of preterm births in the United States increased by 36% in a 22-year period, from 9.4% of births in 1984 to 12.8% in 2006. More recently, from 2006, the percentage of preterm births declined by 4% to 12.3% in 2008 (based on preliminary data) (Fig. 1)23,24; however, the U.S.

percentage of preterm births is still very high when compared with other developed countries.25 For example, in 2004, 1 in 8 infants in the United States were born preterm, compared with 1 in 18 infants in Ireland and Finland, and 1 in 16 infants in France and Sweden.25 The percentage of preterm births varies greatly by race and ethnicity. Data for 2007 are used for race and ethnic comparisons because 2008 preliminary data are not available for all race and ethnic groups.24 In 2007, the percentage of preterm births was 59% greater for non-Hispanic black (18.3%) than for non-Hispanic white women (11.5%; Table 1). Compared with non-Hispanic white women, the percentage of preterm births was also greater for Puerto Rican (14.5%), American Indian (13.9%), Cuban (13.4%), Central and South American (12.1%), and Mexican women (11.9%). The percentage of preterm births was lower for Asian or Pacific Islander (10.9%) than for non-Hispanic white women.26 Trends in the percentage of preterm births from 1990 to 2008 were examined for non-Hispanic white, non-Hispanic black, and Hispanic women. For non-Hispanic white women, the percentage of preterm births increased by 38% from 1990 to 2006 and then decreased by 5% from 2006 to 2008. For non-Hispanic black women, the percentage of preterm births declined by 8% from 1990 to 2000, increased by 6% from 2000 to 2006, and then decreased by 5% from 2006 to 2008. For Hispanic women, the percentage of preterm births increased by 12% from 1990 to 2007 and then decreased by 2% from 2007 to 2008.23,24,26 When examined by gestational age, late preterm births (34-36 weeks of gestation) increased by 25%, whereas births at ⬍34 weeks of gestation increased by 12% from 1990 to 2006. From 2006 to 2008, both groups decreased by 3%.23 The increase in the preterm birth rate from 1990 to 2006 was largest for older mothers and very slight for teenagers.23 For example, the percentage of preterm births increased by 33% for 40- to 44-year-old mothers, and by 67% for 45- to 54-

Race and ethnic disparities in infants in the U.S. year-old mothers. From 2006 to 2008, the preterm birth rate decreased for all age groups younger than 40.23 Other risk factors for preterm birth include multiple pregnancy, low socioeconomic or educational status, unmarried status, hard physical labor or long working hours, short interpregnancy intervals, low body mass index or micronutrient deficiency, and previous preterm birth.20-22,26

Types of Preterm Birth Preterm birth can be separated into different types, with differences in etiologies and risk factors. Approximately 40%45% of preterm births are caused by spontaneous preterm labor, 25%-30% are caused by preterm premature rupture of membranes, and 30%-35% are medically indicated preterm births—in other words, induction of labor or cesarean delivery to deliver the fetus early for medical indications.20 Much research attention has been focused on the etiology and prevention of spontaneous preterm labor20 –22; however, most of the recent increase in the percentage of preterm births has been among medically indicated preterm births.20,22,27,28 The causes of spontaneous preterm labor and preterm premature rupture of membranes are complex but may be related to issues such as infection or inflammation, uteroplacental such as infection or inflammation, uteroplacental vascular disease or hemorrhage, uterine overdistension particularly in the case of multiple pregnancy, and unknown factors.20-22 Cervical insufficiency and short cervical length are also associated with an increased risk of preterm delivery20-22; however, a significant proportion of spontaneous preterm labors occur in otherwise-healthy women with no previously identified risk factors.20-22 With regard to medically indicated preterm births, we used U.S. birth certificate data from 1991 to 2006 to assess the impact of possible changes in the obstetrical management of pregnancy on the preterm birth rate.27 In Fig. 3 the overall percentage of singleton preterm births from 1991 to 2006 is divided into subgroups by method of delivery: spontaneous vaginal, induced vaginal, cesarean delivery with no induction

203 attempt, and cesarean delivery following an induction attempt. From 1991 to 2006 the percentage of singleton preterm births delivered by cesarean delivery increased by 64%, whereas the percentage with induced vaginal deliveries more than doubled. Therefore, although the overall percentage of preterm births was increasing from 1991 to 2006, both the number and percentage of preterm births that were spontaneous vaginal deliveries decreased sharply.27 When examined as a proportion of all preterm births, in 2006 only 51% of singleton preterm births were spontaneous vaginal deliveries, compared with 69% in 1991.27 In addition these figures are conservative, as studies have suggested that induction of labor is underreported in vital statistics data.29 Concern about the impact of medically elective procedures has led several major health insurance groups to limit or prohibit medically elective cesarean deliveries before 39 weeks.30,31 It is too early to tell to what extent initiatives like this have had an impact nationally, but the 4% decrease in the percentage of preterm births from 2006 to 2008 did occur among all methods of delivery— cesarean, induced vaginal, and spontaneous vaginal.23

Infant Mortality After significant decreases during the 1990s, the U.S. infant mortality rate has not declined much since 2000, which has generated concern among researchers and policy makers. In 2007, the U.S. infant mortality rate was 6.75 infant deaths per 1000 live births, compared with a rate of 6.89 in 2000.32,33 Also of concern is the U.S.’s relatively poor and declining international ranking in infant mortality.25 In 2005, the United States ranked 30th in the world in infant mortality, behind most European countries, Canada, Australia, New Zealand, Hong Kong, Singapore, Japan, and Israel.25 Much of the greater infant mortality rate in the United States, when compared with other countries is due to the U.S.’s very high percentage of preterm births, a critical risk factor for infant mortality.25

Figure 3 Percentage of singleton preterm births by method of delivery: United States, 1991-2006.

M.F. MacDorman

204 As with fetal mortality, there are large differences in infant mortality rates by maternal race and ethnicity. The linked birth/infant death data set is used in this analysis because it links the birth certificate and death certificate information for each infant who dies when he or she younger than 1 year of age in the United States. The purpose of the linkage is to use the additional variables and more accurate race and ethnic information from the birth certificate for infant mortality analysis.4 In 2006, the infant mortality rate for non-Hispanic black women was 13.35 infant deaths per 1000 live births, 2.4 times the rate for non-Hispanic white women (5.58) (Table 1). Compared with non-Hispanic white women, the infant mortality rate was 48% greater for American Indian women (8.28), and 44% greater for Puerto Rican women (8.01). In contrast, infant mortality rates for Mexican, (5.34) Cuban (5.08), Central and South American (4.52), and Asian or Pacific Islander (4.55) women were lower than for non-Hispanic white women. Approximately twothirds of all infant deaths occurred in the first 28 days of life—the neonatal period, whereas approximately onethird occurred during the postneonatal period from 1 to 11 months of age.4 As with fetal mortality, infant mortality exhibits a curvilinear relationship with maternal age, with rates for the youngest and oldest women 2-4 times those for women in the lowest risk age group (30-34 years).4 Infant mortality rates are also substantially higher for multiple than for single pregnancies. In 2006, the infant mortality rate for twins was 27.92, nearly 5 times the rate for single births (5.87). The rate for triplets was nearly 12 times, and the rate for quadruplets was 25 times the rate for single births.4 In 2006, the infant mortality rate for mothers born in the 50 states and DC (7.03) was 38% greater than the rate for mothers born elsewhere (5.09). Several hypotheses have been mentioned to explain these differences, including possible differences in migration selectivity, diet and nutrition, social support, and risk behaviors.34,35 Infant mortality rates are also greater for mothers with late or no prenatal care, those who smoke

during pregnancy, and those with less than a high school education.4

The Influence of Preterm Birth on Infant Mortality Preterm infants have a much greater risk of death and disability than term infants. In 2006, the infant mortality rate for very preterm infants (⬍32 weeks of gestation) was 175.94 infant deaths per 1000 live births, 74 times the rate of 2.39 for term infants.4 Although mortality decreases with increasing gestational age, even infants born only a few weeks early have a substantially increased risk of death. For example, the infant mortality rate for late preterm infants (34-36 weeks of gestation) was 7.08, 3 times the rate for term infants. Even within the term period, the mortality rate for infants born at 37-38 weeks of gestation was 47% higher than for infants born at 39-41 weeks of gestation.4 Currently, 29% of U.S. births occur at 37-38 weeks of gestation.26 Because of their much greater risk of death, infants born at the lowest gestational ages have a large impact on overall U.S. infant mortality (Fig. 4). In 2006, more than two-thirds of all infant deaths in the United States occurred to the 13% of infants born preterm, and more than one-half (54%) occurred to the 2% of infants born very preterm.

Leading Causes of Infant Death The 5 leading causes of infant death in 2006 were congenital malformations, followed by disorders related to short gestation and low birthweight not elsewhere classified (short gestation/low birthweight), Sudden infant death syndrome (SIDS), maternal complications of pregnancy, and unintentional injuries (Table 2). From 2000 to 2006, there was a 3% decrease in infant mortality from congenital malformations and a 12% decrease for SIDS, although the latter decline may be caused in part by changes in how coroners and medical examiners certify sudden unexpected infant deaths.4,36,37 In contrast, the infant mortality rate from short gestation/low

Figure 4 Percentage of live births and infant deaths by weeks of gestation: United States, 2006.

Race and ethnic disparities in infants in the U.S.

205

Table 2 Infant Mortality Rates for the 5 Leading Causes of Infant Death by Race and Hispanic Origin of Mother: United States, 2006 Linked File Rates per 100,000 Live Births in Specified Groupause of Death (ICD-10) All causes 1. Congenital malformations, deformations, and chromosomal abnormalities (Q00Q99) 2. Disorders related to short gestation and low birth weight, not elsewhere classified (P07) 3. Sudden infant death syndrome (R95) 4. Newborn affected by maternal complications of pregnancy (P01) 5. Accidents (unintentional injuries) (V01-X59)

Total

NonHispanic White

NonHispanic Black

American Indian

Asisan or Pacific Islander

Total Hispanic*

Mexican

Puerto Rican

Central and South American

668.3 137.1

558.1 126.6

1335.1 174.6

827.7 153.0

455.1 109.1

541.1 142.0

534.3 151.4

800.8 122.5

452.5 117.3

113.5

76.8

301.8

98.5

76.3

85.4

81.6

165.8

69.6

54.6

55.6

103.8

119.4

22.8

27.1

25.5

55.3

15.1

39.3

31.7

89.4

†

23.6

27.9

28.3

55.3

15.1

26.8

25.9

52.8

77.5

12.9

14.8

13.8

†

†

*Includes additional Hispanic origin groups not shown separately. Reliable cause-specific infant mortality rates could not be computed for Cuban women because of the small number of infant deaths (86). †Figure does not meet standards of reliability or precision; based on fewer than 20 deaths in the numerator.

birthweight as a cause of death increased by 5%; and the rate from maternal complications, a cause that is also closely associated with preterm birth, increased by 15% during the period. The infant mortality rate from unintentional injuries also increased by 24% from 2000 to 2006, although much of this increase was among the accidental suffocation and strangulation in bed subcategory, and may represent deaths that might formerly have been classified as SIDS.4,37 There are also large differences in the leading causes of death by race and ethnicity (Table 2). Congenital malformations were the leading cause of infant death for all groups except for non-Hispanic black and Puerto Rican women, for whom short gestation/low birthweight was the leading cause. Infant mortality rates from congenital malformations were 38% greater for non-Hispanic black, and 20% greater for Mexican than for non-Hispanic white women. Infant mortality rates from congenital malformations were 14% lower for Asian or Pacific Islander than for non-Hispanic white women. Infants of non-Hispanic black mothers had the highest mortality rates from short gestation/low birthweight. The rate for non-Hispanic black mothers was nearly 4 times the rate for non-Hispanic white mothers. The rate for Puerto Rican mothers was more than twice the rate for non-Hispanic white mothers. SIDS rates were highest for American Indian and nonHispanic black mothers, 2.1 and 1.9 times those for nonHispanic white mothers, respectively. Compared with non-Hispanic white mothers, SIDS rates were 54% lower for Mexican mothers, 59% lower for Asian or Pacific Islander mothers, and 73% lower for Central and South American mothers. For maternal complications, a cause of death closely asso-

ciated with preterm birth, infants of non-Hispanic black mothers had the highest mortality rate, 2.8 times the rate for non-Hispanic white mothers. The infant mortality rate for Puerto Rican mothers was 74% higher than for non-Hispanic white mothers. Infant mortality rates from maternal complications were 26% lower for Asian or Pacific Islander and 52% lower for Central and South American than for non-Hispanic white women. For American Indian women, the infant mortality rate from unintentional injuries was 3 times the rate for nonHispanic white women. For non-Hispanic black women the rate from unintentional injuries was 2 times that for nonHispanic white women. Infant mortality rates from unintentional injuries were 47% lower for Mexican and 50% lower for Asian or Pacific Islander women than for non-Hispanic white women.

Preterm-Related Causes of Death To better measure the impact of preterm-related infant mortality, the Centers for Disease Control and Prevention has developed a grouping of preterm-related causes of death. A cause of death is considered preterm-related if more than three-quarters of infants whose deaths were attributed to that cause were born preterm, and the cause of death was a direct consequence of preterm birth based on a clinical evaluation and review of the literature. Included, from the 5 leading causes of death, are disorders related to short gestation and low birthweight, not elsewhere classified, and most of the maternal complications of pregnancy category, plus a variety of other causes of death closely associated with prematurity, such as respiratory distress of newborn, bacterial sepsis of newborn, necrotizing entero-

M.F. MacDorman

206

Figure 5 Total and preterm-related infant mortality rates by race and ethnicity of mother: United States, 2006.

colitis of newborn, and others.38,39 In 2006, 36.1% of all infant deaths in the United States were preterm related, up from 34.6% in 2000.4 The impact of preterm-related infant mortality was also considerably higher for some race and ethnic groups. In 2006, 45% of infant deaths to nonHispanic black women, and 41% of infant deaths to Puerto Rican women were preterm-related.4 Figure 5 shows total and preterm-related infant mortality rates by race and ethnicity for 2006. Preterm-related infant mortality rates were 3.4 times higher for non-Hispanic black women and 1.8 times higher for Puerto Rican women, than for non-Hispanic white women. In fact, the preterm-related infant mortality rate for non-Hispanic black women was higher than the total infant mortality rate for non-Hispanic white women. In addition, these estimates of preterm-related infant mortality are actually quite conservative because many cause-of-death categories are not specific enough to establish the etiologic connection to preterm birth with any degree of certainty.38,39

Causes of Death Contributing Most to Racial and Ethnic Disparities in Infant Mortality An examination of cause-specific differences in infant mortality rates among race and ethnic groups can help in understanding overall differences in infant mortality rates among these groups. In this section, we examine causes of death for the 3 race/ethnic groups with elevated infant mortality rates when compared with non-Hispanic white mothers: non-Hispanic black, American Indian, and Puerto Rican mothers. By using methods described elsewhere, we compute the percentage contribution of specific causes of death to the overall race/ethnic difference in infant mortality.4 In 2006, the infant mortality rate for non-Hispanic black women was 13.35, 2.4 times the rate for non-Hispanic white women (5.58; Table 1). When comparing non-Hispanic black and non-Hispanic white infant mortality, we find that preterm-related causes of death accounted for 54% of the

disparity, congenital malformations and SIDS each accounted for 6% of the disparity and unintentional injuries accounted for 3% of the disparity (Fig. 6). Thus, if nonHispanic black infant mortality rates for these 4 causes could be reduced to non-Hispanic white levels, the disparity in infant mortality rates between these 2 groups would be reduced by 70%. The infant mortality rate for American Indian mothers was 8.28, 48% greater than the rate for non-Hispanic white women (5.58). When we examine the impact of disparities in causes of death on the American Indian-white infant mortality gap, we find that SIDS accounted for 24% of the disparity, followed by unintentional injuries (19%), preterm-related causes (12%), and congenital malformations (10%). Thus, if American Indian infant mortality rates for these 4 causes could be reduced to non-Hispanic white levels, the American Indian-white infant mortality gap would be reduced by 64%. The infant mortality rate for Puerto Rican mothers was 8.01, 43% greater than the rate for non-Hispanic white women (5.58), and preterm-related causes were the main contributors to the disparity. Thus, if Puerto Rican infant mortality rates for preterm-related causes could be reduced to non-Hispanic white levels, the Puerto Rican –non-Hispanic white infant mortality gap would be reduced by 62%.

Discussion Infant mortality, fetal mortality, and preterm birth all represent significant health challenges that have shown little recent improvement despite programmatic efforts at the federal, state, and local levels. The rate of decrease in both fetal and infant mortality has slowed in recent years, with little or no decrease since 2000 for infant mortality, and no significant decrease from 2003 to 2005 for fetal mortality. The percentage of preterm births increased by 36% from 1984 to 2006, and then declined by 4% from 2006 to 2008. There are substantial race and ethnic disparities in fetal and infant mortality rates, and in the percentage of preterm

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Figure 6 Contribution of causes of death to the non-Hispanic black - non-Hispanic white infant mortality gap: United States, 2006.

births. Non-Hispanic black women have the highest risk of unfavorable birth outcomes, followed by American Indian and Puerto Rican women. The persistent, and in some cases (infant mortality) increasing racial and ethnic disparities suggest that not all racial and ethnic groups have benefited equally from social and medical advances.4,40,41 Fetal mortality, infant mortality, and preterm birth share many similarities in etiology, risk factors and disease pathways. Risk factors for poor birth outcomes include teen or advanced maternal age, multiple pregnancy, low socioeconomic or educational status, maternal smoking, lack of prenatal care, and unmarried status, among others. However, these risk factors do not explain many adverse outcomes. Infant mortality, fetal mortality, and preterm birth are multifactorial problems with highly interrelated etiologies and prevention strategies. Preventing preterm birth is critical to both lowering the overall infant mortality rate and to reducing race and ethnic disparities.

Acknowledgments The author would like to thank Joyce Martin and T.J. Mathews for contributions to the manuscript.

References 1. Ventura SJ, Abma JC, Mosher WD, et al: Estimated Pregnancy Rates by Outcome for the United States, 1990-2005: An Update. National Vital Statistics Reports; Vol. 58, No. 4. Hyattsville, MD, National Center for Health Statistics, 2009 2. MacDorman MF, Kirmeyer S: Fetal and perinatal mortality, United States, 2005. National Vital Statistics Reports; Vol. 57. No. 8. Hyattsville, MD, National Center for Health Statistics, 2009 3. MacDorman MF, Kirmeyer S: The Challenge of Fetal Mortality. NCHS Data Brief No. 16. Hyattsville, MD, National Center for Health Statistics, 2009 4. Mathews TJ, MacDorman MF: Infant Mortality Statistics from the 2006 Period Linked Birth/Infant Death Data Set: National Vital Statistics Reports; Vol. 58, No. 17. Hyattsville, MD, National Center for Health Statistics, 2010 5. Bateman BT, Simpson LL: Higher rate of stillbirth at the extremes of

6.

7. 8. 9.

10. 11.

12.

13.

14. 15.

16.

17.

18. 19. 20. 21.

22.

reproductive age: A large nationwide sample of deliveries in the United States. Am J Obstet Gynecol 194:840N5, 2006 Reddy UM, Ko CW, Willinger M: Maternal age and the risk of stillbirth throughout pregnancy in the United States. Am J Obstet Gynecol 197: 114, 2006 Smith GCS, Fretts RC: Stillbirth. Lancet 370:1715-1724, 2007 Huang L, Asuve R, Birkett N, et al: Maternal age and risk of stillbirth: A systematic review. CMAJ 187:183-184, 2008 Nabukera SK, Wingate MS, Owen J, et al: Racial disparities in perinatal outcomes and pregnancy spacing among women delaying initiation of childbearing. Matern Child Health J 13:81-89, 2009 Chu SY, Kim SY, Lau J, et al: Maternal obesity and risk of stillbirth: A metaanalysis. Am J Obstet Gynecol 199:e17-e18, 2008 Salihu HM, Dunlop AL, Hedayatzadeh M, et al: Extreme obesity and risk of stillbirth among black and white gravidas. Obstet Gynecol 110: 552-557, 2007 Hogberg L, Cnattingius S: The influence of maternal smoking habits on the risk of subsequent stillbirth: Is there a causal relation? Br J Obstet Gynaecol 114:699-704, 2007 Salihu HM, Sharma PP, Getahun D, et al: Prenatal tobacco use and risk of stillbirth: a case-control and bidirectional case-crossover study. Nicotine Tob Res 10:159-166, 2008 Dudley DJ: Diabetic-associated stillbirth: Incidence, pathophysiology, and prevention. Obstet Gynecol Clin North Am 43:293-307, 2007 Sharma PP, Salihu HM, Kirby RS: Stillbirth recurrence in a population of relatively low-risk mothers. Paediatr Perinat Epidemiol 21(suppl 1):24-30, 2007 Gray R, Quigley MA, Hockley C, et al: Caesarean delivery and risk of stillbirth in subsequent pregnancy: A retrospective cohort study in an English population. Br J Obstet Gynaecol 114:264-270, 2007 Rasmussen S, Albrechtsen S, Irgens LM, et al: Unexplained antepartum fetal death in Norway, 1985-97: Diagnostic validation and some epidemiologic aspects. Acta Obstet Gynecol Scand 82:109-115, 2003 Silver RM: Fetal death. Obstet Gynecol 109:153-167, 2007 Reddy UM: Prediction and prevention of recurrent stillbirth. Obstet Gynecol 110:1151-1164, 2007 Goldenberg RL, Culhane JF, Iams JD: Epidemiology and causes of preterm birth. Lancet 371:75-83, 2009 Behrman RE, Butler AS (eds): Preterm Birth: Causes, Consequences, and Prevention. Washington, DC, Board of Health Sciences Policy, Institute of Medicine, National Academies Press, 2005 Creasy RK, Resnik R, Iams JD et al (eds): Maternal-Fetal Medicine, Principles and Practice. 6th ed. Philadelphia, Saunders-Elsevier Publishers, 2009

208 23. Martin JA, Osterman MJK, Sutton PD: Are Preterm Births on the Decline in the United States? Recent Data from the National Vital Statistics System. NCHS Data Brief No. 39. Hyattsville, MD, National Center for Health Statistics, 2010 24. Hamilton BE, Martin JA, Ventura SV: Births: Preliminary Data for 2008: National Vital Statistics Reports; Vol. 58, No. 16. Hyattsville, MD, National Center for Health Statistics, 2010 25. MacDorman MF, Mathews TJ: Behind International Rankings of Infant Mortality: How the United States Compares with Europe. NCHS Data Brief No. 23. Hyattsville, MD, National Center for Health Statistics, 2009 26. Martin JA, Hamilton BE, Sutton PD, et al: Births, Final Data for 2007. National Vital Statistics Reports; Vol. 58, No. 24. Hyattsville, MD, National Center for Health Statistics, 2010 27. MacDorman MF, Declercq E, Zhang J: Obstetrical intervention and the singleton preterm birth rate in the United States from 1991-2006. Am J Public Health 100:2241-2247, 2010 28. Bettegawda VR, Dias T, Davidoff MJ, et al: The relationship between cesarean delivery and gestational age among US singleton births. Clin Perinatol 35:309-324, 2008 29. Zhang J, Troendle J, Reddy UM, et al, for the Consortium on safe labor: Contemporary cesarean delivery practice in the United States. Am J Obstet Gynecol 203:326.e1-326.e10, 2010 30. Oshiro BT, Henry E, Wilson J, et al: Decreasing elective deliveries before 39 weeks of gestation in an integrated health care system. Obstet Gynecol 113:804-811, 2009 31. Clark SL, Frye DR, Meyers JA, et al: Reduction in elective delivery at ⬍39 weeks of gestation: Comparative effectiveness of 3 approaches to change and the impact on neonatal intensive care admission and stillbirth. Am J Obstet Gynecol 203:449.e1-6, 2010

M.F. MacDorman 32. MacDorman MF, Mathews TJ: Recent Trends in Infant Mortality in the United States. NCHS Data Brief No. 9. Hyattsville, MD, National Center for Health Statistics, 2008 33. Xu J, Kochanek KD, Murphy SL, et al: Deaths: Final Data for 2007: National Vital Statistics Report; Vol. 58, No. 19. Hyattsville, MD, National Center for Health Statistics, 2010 34. Singh GK, Miller BA: Health, life expectancy, and mortality patterns among immigrant populations in the United States. Can J Public Health 95:I14-I21, 2004 35. Liu KL, Laraque F: Higher mortality rate among infants of US-born mothers compared to foreign-born mothers in New York City. J Immigr Minor Health 8:281-289, 2006 36. Malloy MH, MacDorman MF: Changes in the classification of sudden unexpected infant deaths: United States, 1992-2001. Pediatrics 115: 1247-1253, 2005 37. Shapiro-Mendoza CK, Kimball M, Tomashek KM, et al: US infant mortality trends attributable to accidental suffocation and strangulation in bed from 1984 through 2004: Are rates increasing? Pediatrics 123:533538, 2009 38. Callaghan WD, MacDorman MF, Rasmussen SA, et al: The contribution of preterm birth to infant mortality rates in the United States. Pediatrics 118:1566-1573, 2006 39. MacDorman MF, Callaghan WM, Mathews TJ, et al: Trends in pretermrelated infant mortality by race and ethnicity, United States, 19992004. Int J Health Serv 37:635-641, 2007 40. Krieger N, Rehkopf DH, Chen JT, et al: The fall and rise of US inequities in premature mortality: 1960-2002. PLoS Med 5:e46, 2008 41. Kramer MR, Hogue CR: What causes racial disparities in very preterm birth? A biosocial perspective. Epidemiol Rev 31:84-98, 2009