Overview of Mortality and Morbidity

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Chapter 87 Overview of Mortality and Morbidity

The risk for mortality in fetuses and neonates is very high around the time of birth. The perinatal period is most often defined as the period from the 28th wk of gestation through the 7th day after birth. The neonatal period is defined as the 1st 28 days after birth and may be further subdivided into the very early (birth to less than 24 hr), early (birth to <7 days), and late neonatal periods (7 days to <28 days). Infancy is defined as the 1st year after birth.

Perinatal mortality is influenced by prenatal, maternal, and fetal conditions and by circumstances surrounding delivery. Perinatal deaths are associated with intrauterine growth restriction (IUGR); conditions that predispose the fetus to asphyxia, such as placental insufficiency; severe congenital malformations; and overwhelming early-onset neonatal infections (Table 87-1). The major causes of neonatal mortality are prematurity/low birthweight (LBW) and congenital anomalies. Mortality is highest during the 1st 24 hr after birth. Neonatal mortality (4.27/1,000 in 2008) accounts for about two thirds of all infant deaths (deaths before 1yr of age). Neonatal and postneonatal mortality rates in the USA have declined or remained stable (Fig. 87-1). Factors related to the decline in mortality include improved obstetric and neonatal intensive care management with a significant reduction in birthweight-specific neonatal mortality (Fig. 87-2). Further reduction in neonatal mortality will depend on prevention of preterm delivery and LBW, prenatal diagnosis and early management of congenital anomalies, and effective diagnosis and treatment of diseases that result from adverse factors during pregnancy, labor, and/or delivery (see Table 87-1). In the USA each year, approximately 6 million pregnancies, 4 million live births, 19,000 neonatal deaths, and 28,000 infant deaths occur. Ten per cent of births are to teenage women between the ages of 15 and 19 yr, a proportion that has been decreasing for about 35 yr (Fig. 87-3). Births to girls 10-14 yr, very young mothers who are at great social and medical risk, declined substantially over this period. The proportion of deaths to unmarried women was 40.6% in 2008, the highest ever in U.S. history.

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Figure 87-2 Neonatal mortality, by birthweight categories, for black (filled circles) and white (open circles) infants in the United States. Solid lines denote data for 1989; dashed lines are for 1997. Data shown are for births of newborn infants weighing <2,250 g only.

(From Demissie K, Rhoads GG, Ananth CV, et al: Trends in preterm birth and neonatal mortality among blacks and whites in the United States from 1989 to 1997, Am J Epidemiol 154:307–315, 2001.)

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Figure 87-3 Birthrates for teenagers by age, USA, final for 1980-2006 and preliminary for 2007.

(From Hamilton BE, Martin JA, Ventura SJ: Births: preliminary data for 2007, Natl Vital Stat Rep 57:12:1–23, 2009.)

Infant mortality rates (deaths occurring from birth to 12 mo per 1,000 live births) vary by country; in 2008, rates were lowest in Hong Kong (1.8/1,000 births), moderate in the USA (6.6/1,000), and highest in developing countries (30-150/1,000). Medical, socioeconomic, and cultural factors influence perinatal and neonatal mortality. Preventive variables such as health education, prenatal care, nutrition, social support, risk identification, and obstetric care can effectively reduce perinatal, neonatal, and infant mortality. A number of reasons can explain in part the relatively higher infant mortality in the USA than in other countries. There is evidence of differential reporting of live births versus fetal deaths or stillbirths among countries. Many countries do not report as live births those of infants as mature as up to 27 wk if they die early after birth. The reporting of vital events in the USA is more complete than in many countries, including developed countries. This situation in part explains the larger proportion of LBW/preterm infants in the USA than in other countries. Increases in recorded preterm live births, especially of the most immature infants (<500 g BW) in the USA, result in increases in both neonatal and infant mortality rates. Nonetheless, continuing health care disparities in part account for the higher infant mortality rate in the USA. Infants of African-American women continue to have a high infant mortality rate (13.6/1000), which is more than twice the rates of infants of white (5.6/1000) and Hispanic mothers (5.5/1000).

In the USA, ∼50% of infant deaths in 2008 were due to four conditions (classified according to the International Classification of Diseases, 10th revision): congenital malformations (20.1%), disorders relating to prematurity and unspecified LBW (16.9%), sudden infant death syndrome (SIDS) (8.2%), and newborns affected by maternal complications of pregnancy (6.3%). LBW (as a result of preterm delivery and/or IUGR) is a major determinant of both neonatal and infant mortality rates and, together with congenital anomalies (cardiac, central nervous system, respiratory), contributes significantly to childhood morbidity. In developing countries, LBW/prematurity, birth asphyxia, and infections are the major causes of infant deaths.

The LBW rate (infants weighing ≤ 2,500 g at birth each year) in the USA increased from 6.6% to 8.2% between 1981 and 2008, whereas the very low birthweight (VLBW) rate (infants weighing ≤1,500 g at birth) increased from 1.1% to 1.46% of all births. In the past decade, LBW has increased among white infants, mainly because of a rise in the number of multiple births (often associated with assisted reproduction) (Fig. 87-4). Nonetheless, LBW and VLBW rates remain highest among black infants. Reasons for the racial disparity in LBW remain unclear. Despite advances in prenatal and obstetric care, racial disparity in birthweight persists, thus suggesting the need for novel prevention programs. Furthermore, although preterm LBW survival is better among black neonates (see Fig. 87-2), overall neonatal and infant mortality rates remain highest among blacks (Fig. 87-5), even for infants born to extremely low-risk mothers (married, aged 20-34 yr, ≥13 yr of education, adequate prenatal care, no medical risk factors, no alcohol or tobacco use during pregnancy). A reduction in the racial disparity in mortality is an important public health issue reflected in Healthy People 2010, the U.S. national health objectives for the year 2010.

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Figure 87-4 Preterm birthrates, USA, final for 1990-2006 and preliminary for 2007.

(From Hamilton BE, Martin JA, Ventura SJ: Births: preliminary data for 2007, Natl Vital Stat Rep 57:12:1–23, 2009.)