Trends in the Well-Being of America's Children and Youth, 2000. HC 2.2 Low and Very Low Birthweight

01/01/2000

Low Birthweight

Babies born weighing less than 2,500 grams (5lb. 8oz.) face an increased risk of physical and developmental complications and death.22 These babies account for four-fifths of all neonatal deaths (deaths under 28 days of age) and are 24 times more likely to die during the first year than are heavier infants.23

Although slight declines are seen in the early 1980s, overall the percentage of all infants born at low birthweight has increased steadily since 1985, when 6.8 percent of infants were born at low birthweight, compared with 7.6 percent in 1999 (see Table HC 2.2.A).

Smoking. Babies born to mothers who smoke during pregnancy are at greatly elevated risk of low birthweight, a finding documented in birth certificate data as well as in numerous other studies.24 In 1998, 12 percent of infants born to smokers weighed less than 2,500 grams (5lb. 8oz.) compared with 7.2 percent of births to nonsmokers (See Figure HC 2.2.A). This substantial differential is found for every race and Hispanic origin group (See Figure HC 2.2.A). The low birthweight risk is heightened as the number of cigarettes increases, “although low birthweight is elevated even among babies born to the lightest smokers (one to five cigarettes daily).” “Advancing maternal age exacerbates the risk, probably a consequence of the much greater cigarette consumption among older women.”25

Differences by Race and Ethnicity. Low birthweight rates are substantially higher among black infants than among other races and Hispanics. The percentages of low birthweight infants among whites, American Indians/Alaska Natives, Asians/Pacific Islanders, and Hispanics have remained within 1 percentage point of each other and have mostly hovered around 6 to 7 percent over the last two decades, compared to around 13 percent for blacks.

Among Asians/Pacific Islanders and Hispanics, there are important subgroup differences. Since 1970, Chinese women have consistently had the lowest percentage of low-weight births, and Filipino women have had the highest among Asian/Pacific Islander women. Among Hispanics, Mexican American women have generally had the lowest percentage of low birthweight infants, and Puerto Rican women have had the highest (see Table HC 2.2.A).

Differences by Age. For women in all age groups, there was a decline in the percentage of low-weight births between 1970 and 1985. Since 1985, however, that percentage increased slightly across nearly all age groups. The following trends, illustrated in Table HC 2.2.A, are particularly noteworthy:

  • Women under age 15 consistently have the highest rates of low-weight births of any age group (see Figure HC 2.2.B).
  • For women in all other age groups, rates of low-weight births have generally stayed within 1.5 percentage points of their 1970 rate.
  • Women between the ages of 25 and 29 consistently have the lowest rates of lowweight births.

Multiple births. Multiple births are more likely than singletons to be born either preterm or low birthweight (See Figure HC2.2.C). Multiples comprised only 3 percent of all births in 1998, but 21 percent of all low birthweight infants and 24 percent of very low birthweight. Multiple birth rates generally rise with increasing maternal age, with the rate peaking for mothers 45 to 54 years of age. The rising multiple birth rate and the accompanying high risk for these births has increasingly influenced measures of perinatal health at the national and State levels.26

Very Low Birthweight

Babies born weighing less than 1,500 grams (3lb. 4oz.) are at particularly high risk of severe physical and developmental complications and death. Advances in medical technology in recent years have made it possible for increasing numbers of very low birthweight infants to survive; however, these babies are 96 times more likely to die during the first year of life than babies weighing at least 2,500 grams.27

The percentage of infants born at very low birthweight has increased steadily since the early 1980s, by 25 percent overall since 1981 (see Table HC 2.2.C). Between 1970 and 1989 (not shown), 1.2 percent of all infants were classified as very low birthweight. The proportion then increased to 1.27 percent in 1990, and to 1.45 percent in 1998.

Differences by Race and Ethnicity. The percentage of babies born at very low birthweight varies by race and Hispanic origin (see Table HC 2.2.C). For white, Hispanic, American Indian/Alaska Native, and Asian/Pacific Islander infants, the percentage of very low-weight births was about 1 percent in 1998. However, the percentage of black infants born at very low birthweight is considerably higher. In 1970, 2.4 percent of all infants born to black mothers weighed 1,500 grams or less, a percentage that has increased to 3.1 in 1998. The percentage of very low birthweight has increased steadily for all groups since the early 1980’s.

Differences by Age. A woman’s age is an important factor in the likelihood of very low birthweight, particularly at the youngest ages. The percentage of very low birthweight infants born to women under age 15 was 3.3 percent in 1998. The percentage of very low birthweight births among women ages 15 through 19 is lower than the proportion of such births to their younger counterparts but remains slightly higher than the proportion observed for women ages 20 and older, (see Table HC 2.2C).

Table HC 2.2.A Low birthweighta infants as a percentage of all infants born in the United States by mother’s race/ethnicityb and by age: Selected years, 1970-1999

  1970 1975 1980 1985 1990 1995 1996 1997 1998 1999
Total 7.9 7.4 6.8 6.8 7.0 7.3 7.4 7.5 7.6 7.6
Race/ethnicity
Whitec 6.9 6.3 5.7 5.7 5.6 6.2 6.4 6.5 6.6 6.6
Blackc 13.9 13.2 12.7 12.7 13.3 13.2 13.1 13.1 13.2 13.1
American Indian/Alaskan Native 8.0 6.4 6.4 5.9 6.1 6.6 6.5 6.8 6.8
Asian/Pacific Islander 6.7 6.2 6.5 6.9 7.1 7.2 7.4
Chinese 6.7 5.3 5.2 5.0 4.7 5.3 5.0 5.1 5.3
Japanese 9.0 7.5 6.6 6.2 6.2 7.3 7.3 6.8 7.5
Filipino 10.0 8.1 7.4 7.0 7.3 7.8 7.9 8.3 8.2
Hawaiian and part Hawaiian 7.2 6.5 7.2 6.8 6.8 7.2 7.2
Other Asian or Pacific Islander 6.8 6.2 6.7 7.1 7.4 7.5 7.8
Hispanic originb, d 6.1 6.2 6.1 6.3 6.3 6.4 6.4 6.4
Mexican American 5.6 5.8 5.6 5.8 5.9 6.0 6.0
Puerto Rican 9.0 8.7 9.0 9.4 9.2 9.4 9.7
Cuban 5.6 6.0 5.7 6.5 6.5 6.8 6.5
Central and South American 5.8 5.7 5.8 6.2 6.0 6.3 6.5
Other and unknown Hispanic 7.0 6.8 6.9 7.5 7.7 7.9 7.6
Age
Under age 15 16.6 14.1 14.6 12.9 13.3 13.5 12.8 13.6 13.1 12.8
15-19 years 10.5 10.0 9.4 9.3 9.3 9.3 9.3 9.5 9.5 9.6
20-24 years 7.4 7.1 6.9 6.9 7.1 7.3 7.4 7.4 7.5 7.6
25-29 years 6.9 6.1 5.8 5.9 6.2 6.4 6.5 6.6 6.7 6.7
30-34 years 7.5 6.8 5.9 6.1 6.4 6.7 6.8 6.9 7.0 7.0
35-49 yearse 8.8 8.4 7.2 7.1 7.4 8.3 8.3 8.6 8.7 8.7

a Before 1979, low birthweight was defined as infants weighing 2,500 grams (5lb. 8oz.) or less. From 1979 and beyond, low birth weight defined as infants weighing less than 2,500 grams (5lb. 8oz.).

b Birth figures for Hispanic infants are based on data from 22 states that reported Hispanic origin on the birth certificate in 1980, 23 states and the District of Columbia in 1985, 48 states and the District of Columbia in 1990, 49 states and the District of Columbia in 1992, and 50 states and the District of Columbia since 1993.

c Excludes persons of Hispanic origin after 1990.

d Persons of Hispanic origin may be of any race.

e Data for 1997 and 1998 are for ages 35-54 years.

Sources: Curtin & Martin, 2000; Ventura, et al., 2000; Ventura, et al., 1999, Births, Tables 24, 25, and 45; Centers for Disease Control, National Center for Health Statistics, 1998, Health, United States, 1998, Table 11; and unpublished tabulations, Division of Vital Statistics, National Center for Health Statistics.


Table HC 2.2.B Percent low birthweighta among singletons by race/Hispanic origin of mother: 1989-98

  1989d 1990c 1991b 1992b 1993 1994 1995 1996 1997 1998
Total 6.00 5.90 5.99 5.93 6.05 6.05 6.05 6.03 6.08 6.05
Non-Hispanic White 4.60 4.56 4.61 4.59 4.70 4.79 4.87 4.90 4.95 4.91
Non-Hispanic Black 12.22 11.92 12.15 11.91 11.90 11.79 11.66 11.55 11.46 11.44
Hispanic 5.35 5.23 5.29 5.22 5.34 5.37 5.36 5.34 5.43 5.40

a Low birthweight is less than 2,500 grams or 5lb 8oz.

b Excludes data for New Hampshire, which did not require reporting of Hispanic origin of mother.

c Excludes data for New Hampshire and Oklahoma which did not require reporting of Hispanic origin of mother.

d Excludes data for Louisiana, New Hampshire, and Oklahoma which did not require reporting of Hispanic origin of mother.

Sources: Martin & Park, Trends in twin and triplet births: 1980-1997; National Vital Statistics Reports 47(24). Hyattsville, MD: National Center for Health Statistics; Ventura, et al., 2000, Births; Ventura, et al., 1999, Births, Tables 24, 25 and 45


Figure HC 2.2.A Percentage of children born with low birthweight,a by mother’s smoking status and age, race and Hispanic origin, 1998

Figure HC 2.2.A Percentage of children born with low birthweight,a by mother’s smoking status and age, race and Hispanic origin, 1998

Figure HC 2.2.A continued Percentage of children born with low birthweight,a by mother’s smoking status and age, race and Hispanic origin, 1998

Figure HC 2.2.A continued Percentage of children born with low birthweight,a by mother’s smoking status and age, race and Hispanic origin, 1998

a Low birthweight defined as infants weighing less than 2,500 grams (5lb. 8oz.).

b Data for smokers under 15 years did not meet standards of reliability or precision; based on fewer than 20 births in numerator or denominator.

Sources: Ventura, et al., 2000, Births, Tables 24, 25, and 45.


Figure HC 2.2.B Low birthweighta infants as a percentage of all infants born in the United States, by age of mother: 1998

Figure HC 2.2.B Low birthweighta infants as a percentage of all infants born in the United States, by age of mother: 1998

a Low birthweight defined as infants weighing less than 2,500 grams (5lb. 8oz.).

Sources: Ventura, et al., 1999, Births, Table 45.


Figure HC 2.2.C Percentage of children born with low birthweight by plurality and age of mother: United States, 1998

Figure HC 2.2.C Percentage of children born with low birthweight by plurality and age of mother: United States, 1998

Source: Unpublished tabulation, Division of Vital Statistics, National Center for Health Statistics, 2000.


Table HC 2.2.C Very low birthweighta infants as a percentage of all infants born in the United States, by mother's race/ethnicityb and by age. Selected years: 1970-1998

  1970 1975 1980 1985 1990 1995 1996 1997 1998
Total 1.17 1.16 1.15 1.21 1.27 1.35 1.37 1.42 1.45
Race/ethnicityb
Whitec 0.95 0.92 0.90 0.94 0.93 1.04 1.08 1.12 1.15
Blackc 2.40 2.40 2.48 2.71 2.93 2.98 3.02 3.05 3.11
American Indian/Alaska Nativec 0.98 0.95 0.92 1.01 1.01 1.10 1.21 1.19 1.24
Asian/Pacific Islanderc 0.92 0.85 0.87 0.91 0.99 1.05 1.10
Chinese 0.80 0.52 0.66 0.57 0.51 0.67 0.64 0.74 0.75
Japanese 1.48 0.89 0.94 0.84 0.73 0.87 0.81 0.78 0.84
Filipino 1.08 0.93 0.99 0.86 1.05 1.13 1.20 1.29 1.35
Hawaiian and part Hawaiian 1.05 1.03 0.97 0.94 0.97 1.41 1.53
Other Asian or Pacific Islander 0.96 0.91 0.92 0.91 1.04 1.07 1.12
Hispanic origind 0.98 1.01 1.03 1.11 1.12 1.13 1.15
Mexican American 0.92 0.97 0.92 1.01 1.01 1.02 1.02
Puerto Rican 1.29 1.30 1.62 1.79 1.70 1.85 1.86
Cuban 1.02 1.18 1.20 1.19 1.35 1.36 1.33
Central and South American 0.99 1.01 1.05 1.13 1.14 1.17 1.23
Other and unknown Hispanic 1.01 0.96 1.09 1.28 1.48 1.35 1.38
Age
Under age 15 3.10 3.40 3.10 3.20 3.15 3.16 3.06 3.28
15-19 years 1.80 1.70 1.80 1.80 1.74 1.72 1.78 1.81
20-24 years 1.10 1.10 1.20 1.30 1.31 1.32 1.37 1.38
25-29 years 0.90 1.00 1.00 1.10 1.16 1.22 1.24 1.27
30-34 years 1.00 1.00 1.10 1.20 1.24 1.26 1.33 1.37
35-49 yearse 1.20 1.20 1.30 1.40 1.58 1.65 1.68 1.71

a Before 1979, very low birthweight defined infants weighing 1,500 grams (3lb. 4oz.) or less. From 1979 and beyond, very low birthweight defined as infants weighing less than 1,500 grams (3lb. 4oz.).

b Birth figures for Hispanic infants are based on data from 22 states that reported Hispanic origin on the birth certificate in 1980, 23 states and the District of Columbia in 1985, 48 states and the District of Columbia in 1990, 49 states and the District of Columbia in 1992, and 50 states and the District of Columbia since 1993.

c Includes persons of Hispanic origin until 1990. Beginning in 1990, persons of Hispanic origin are not included.

d Persons of Hispanic origin may be of any race.

e Data for 1997 and 1998 are for ages 35-54 years.

Sources: Ventura, et al., 2000, Births; Ventura, et al., 1999; Natality 1996, Tables 24, 25, and 45; Centers for Disease Control, National Center for Health Statistics, 2000, Health, Table 12; and unpublished tabulations, Division of Vital Statistics, National Center for Health Statistics.


26 Ibid.

27 Mathews, Curtin, & MacDorman, 2000.

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