Health: Adverse Birth Outcomes
Methods
Indicator
H12. Percentage of babies born preterm, by race/ethnicity, 1993-2019.
H13. Percentage of babies born at term with low birth weight, by race/ethnicity, 1993-2019.
Summary
Since 1960, the National Center for Health Statistics, a division of the Centers for Disease
Control and Prevention, has compiled birth certificate registration data from states and other U.S.
jurisdictions. The National Vital Statistics System (NVSS) online database includes birth
certificate data for virtually all U.S. births from 1968 to 2019. Indicator H12 uses the NVSS data
from 1993 to 2019 to calculate the percentages of babies that are born preterm, defined as a
period of gestation of less than 37 completed weeks. Indicator H13 uses the NVSS data from
1993 to 2019 to calculate the percentages of babies that are both born at term, defined as a period
of gestation of at least 37 completed weeks, and have low birth weight, defined as a weight less
than 2,500 grams (5 pounds, 8 ounces). Tabulated results give the percentages of preterm and
term low birth weight babies by calendar year and maternal race/ethnicity.
Supplementary Tables: Tables H12a and H13a give the percentages of preterm and term low
birth weight babies by calendar year and maternal age group (< 20, 20-39, and 40+). Tables
H12b and H13b give the percentages of preterm and term low birth weight babies by calendar
year and plurality (all, singleton, multiple).
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Data Summary
The following table summarizes the number of data points that were used to support Indicators H12 and H13. For H12, for example,
that is gestation period. For H13, both gestation period and birth weight are used.
H12. Percentage of babies born preterm, by race/ethnicity, 1993-2019.
H13. Percentage of babies born at term with low birth weight, by race/ethnicity, 1993-2019.
Data
U.S. birth certificates
Year
1993
1994
1995
1996
1997
1998
1999
2000
2001
Birth certificates
4,004,523
3,956,925
3,903,012
3,894,874
3,884,329
3,945,192
3,963,465
4,063,823
4,031,531
Missing
35,888
35,124
36,501
40,687
38,503
40,433
42,987
43,392
39,874
gestation period
(0.9%)
(0.9%)
(0.9%)
(1.0%)
(1.0%)
(1.0%)
(1.1%)
(1.1%)
(1.0%)
Missing
gestation period
39,074
38,026
38,897
43,321
40,810
43,045
45,258
45,500
41,784
and/or birth
weight
(1.0%)
(1.0%)
(1.0%)
(1.1%)
(1.1%)
(1.1%)
(1.1%)
(1.1%)
(1.0%)
Years
2002
2003
2004
2005
2006
2007
2008
2009
2010
Birth certificates
4,027,376
4,096,092
4,118,907
4,145,619
4,273,225
4,324,008
4,255,156
4,137,836
4,007,105
Missing
41,295
43,883
43,047
29,585
25,729
20,197
14,118
11,618
10,350
gestation period
(1.0%)
(1.1%)
(1.0%)
(0.7%)
(0.6%)
(0.5%)
(0.3%)
(0.3%)
(0.3%)
Missing
gestation period
43,099
46,887
46,285
33,027
29,358
24,128
17,388
14,588
13,620
and/or birth
weight
(1.1%)
(1.1%)
(1.1%)
(0.8%)
(0.7%)
(0.6%)
(0.4%)
(0.4%)
(0.3%)
Years
2011
2012
2013
2014
2015
2016
2017
2018
2019
Birth certificates
3,961,220
3,960,796
3,940,764
3,998,175
3,988,733
3,956,112
3,864,754
3,801,534
3,757,582
Missing
9,303
8,398
7,483
3,299
2,975
3,513
2,827
2,571
2,538
gestation period
(0.2%)
(0.2%)
(0.2%)
(0.1%)
(0.1%)
(0.1%)
(0.1%)
(0.1%)
(0.1%)
Missing
gestation period
12,070
11,571
11,184
5,876
5,926
6,954
4,945
4,719
5,306
and/or birth
weight
(0.3%)
(0.3%)
(0.3%)
(0.1%)
(0.1%)
(0.2%)
(0.1%)
(0.1%)
(0.1%)
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National Vital Statistics System (NVSS) Natality Data
The National Vital Statistics System (NVSS) is maintained by the National Center for Health
Statistics, a division of the Centers for Disease Control and Prevention. The NVSS compiles
national registration certificate data for births, deaths, marriages, divorces, and fetal deaths
provided by various jurisdictions, including states. This indicator uses NVSS birth data to
determine preterm and term low birth weight births.
For 1993- 2006, Indicator H12 uses the gestation period variable GESTAT3 (GESTREC3 from
2003 to 2006) coded as follows:
• 1 = Under 37 weeks
• 2 = 37 weeks and over
• 3 = Not stated
This variable is a recode of the variable DGESTAT (COMBGEST from 2003 to 2017)
that ranges from 17 to 47 and provides the number of completed weeks of gestation of the
mother. For most of the births in the years 1993-2006 (e.g., 94% of births in 2006), the gestation
period is based on the date of the last menstrual period. A preterm birth is defined as a birth with
GESTAT3 = 1. Birth certificates with an unknown gestation period (GESTAT3 = 3) were
excluded from the calculation of Indicator HI2.
For 2007-2013, Indicator H12 uses the gestation period variable ESTGEST which is the obstetric
or clinical gestation estimate and is coded as follows:
• 17 to 47 = Completed weeks of gestation
• 99 = Unknown or not stated
Birth certificates with an unknown gestation period (ESTGEST = 99) were excluded from the
calculation of Indicator HI2.
For 2014-2019, Indicator H12 uses the gestation period variable OEGest_R3 which is calculated
from the obstetric or clinical gestation estimate and is coded as follows:
• 1 = Under 37 weeks
• 2 = 37 weeks and over
• 3 = Not stated
This variable is a recode of the variable OEGest Comb that ranges from 17 to 47 and provides
the number of completed weeks of gestation of the mother. Birth certificates with an unknown
gestation period (OEGest_3 = 3) were excluded from the calculation of Indicator H12.
Indicator HI3 uses the same gestation period variable GESTAT3 (GESTREC3 from 2003 to
2006, ESTGEST from 2007 to 2013, and OEGest_R3 from 2014 to 2019) and the birth weight
variable BIRWT4 (BWTR4 for 2003 to 2019) coded as follows:
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• 1 = 1499 grams or less
• 2 = 1500 - 2499 grams
• 3 = 2500 grams or more
• 4 = Unknown or not stated
This variable is a recode of the variable DBIRWT (DBWT for 2004 to 2019) that ranges from
0227 to 8165 and gives the birth weight in grams. A term low birth weight birth has a gestation
period of 37 or more completed weeks and a birth weight of less than 2,500 grams. Thus, for
1996-2002, a term low birth weight birth is defined by GESTAT3 = 2 and BIRWT4 = 1 or 2.
Birth certificates with an unknown gestation period (GESTAT3 = 3) and/or an unknown birth
weight (BIRWT4 = 4) were excluded from the calculation of Indicator HI 3.
The birth plurality used the variable DPLURAL, coded as follows:
• 1 = Single
• 2 = Twin
• 3 = Triplet
• 4 = Quadruplet
• 5 = Quintuplet or higher
Singleton births are defined as births with DPLURAL = 1. Multiple births are defined as births
with DPLURAL > 2. In rare cases (e.g., 0.004 % of births in 2019) the plurality was not reported
on the birth certificate and the value of DPLURAL was imputed to be 1 (singleton birth).
Age, Race and Ethnicity
The mother's age, race, and ethnicity were obtained from each of the natality files that were
regrouped by NVSS into categories, as follows:
Years 1993-2002
o Mother's Age: The mother's age for 1993-2002 is characterized by the variable DMAGE.
This variable ranges from 10 to 54 and gives the age of mother in single years. For these
analysis, the following age groups for the mother were defined:
• Mother's age less than 20 years (DMAGE < 20);
• Mother's age between 20 and 39 (20 < DMAGE < 40); and
• Mother's age is 40 or greater (DMAGE > 40).
o Mother's Race and Hispanic origin: The mother's race for 1993-2002 is characterized by
the variable MRACE. MRACE is given the following values for the U.S. state and
Washington DC data used for these analyses. For 1993-2002, multiple race responses
were not available.
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MRACE
01 .
.. White
02 .
.. Black
03 .
.. American Indian (includes Aleuts and Eskimos)
04 .
.. Chinese
05 .
.. Japanese
06 .
.. Hawaiian (includes part-Hawaiian)
07 .
.. Filipino
18 .
.. Asian Indian
28 .
.. Korean
38 .
.. Samoan
48 .
.. Vietnamese
58 .
.. Guamanian
68 .
.. Other Asian or Pacific Islander in areas reporting codes 18-58
78 .
.. Combined other Asian or Pacific Islander, includes codes 18-68 for areas that do
not report them separately
The mother's Hispanic origin for 1993-2002 is characterized by the variable ORMOTH.
ORMOTH assumes the following values:
ORMOTH
0 ... Non-Hispanic
1 ... Mexican
2 ... Puerto Rican
3 ... Cuban
4 ... Central or South American
5 ... Other and unknown Hispanic
9 ... Origin unknown or not stated
Based on the above data, the following categories of the mother's race/ethnicity were defined:
• White non-Hispanic (MRACE = 1 and ORMOTH = 0);
• Black non-Hispanic (MRACE = 2 and ORMOTH = 0);
• American Indian/Alaskan Native (AIAN) non-Hispanic (MRACE = 3 and ORMOTH
=0);
• Asian or Pacific Islander (API) non-Hispanic (MRACE is 4, 5, 6, 7, 18, 28, 38, 48,
58, 68, or 78 and ORMOTH = 0);
• Hispanic Mexican American (ORMOTH =1);
• Hispanic Puerto Rican (ORMOTH = 2);
• All Hispanic (ORMOTH = 1, 2, 3, 4, or 5); and
• Unknown ethnicity - (ORMOTH = 9).
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In approximately 0.5% of the birth certificate records, the mother's race was not stated. In those
cases, if the father's race was stated, then the father's race was used to impute the mother's race.
Otherwise, the mother's race was imputed from the mother's race on the preceding record with a
known mother's race. Thus, a mother's race was assigned to all the records.
Year 2003
o Mother's Age: The mother's age for 2003 is characterized by the variable MAGER41.
This variable is encoded as follows:
MAGER41
01 = Under 15 years
02 = 15 years
03 = 16 years
04 = 17 years
39 = 52 years
40 = 53 years
41 = 54 years
o For these analyses, the following age groups for the mother were defined:
• Mother's age less than 20 years (MAGER41 < 7);
• Mother's age between 20 and 39 (7 < MAGER41 < 27); and
• Mother's age is 40 or greater (MAGER41 > 27).
o Mother's Race and Hispanic origin: The mother's race for 2003 is characterized by two
variables MRACE and MBRACE for the U.S. state and Washington DC data used for
these analyses. MRACE is used for states and years where multiple race responses are
not available, and MBRACE is used for states and years where multiple race responses
are available.
MRACE
01 ... White
02 ... Black
03 ... American Indian (includes Aleuts and Eskimos)
04 ... Chinese
05 ... Japanese
06 ... Hawaiian (includes part-Hawaiian)
07 ... Filipino
18 ... Asian Indian
28 ... Korean
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38 ... Samoan
48 ... Vietnamese
58 ... Guamanian
68 ... Other Asian or Pacific Islander in areas reporting codes 18-58
78 ... Combined other Asian or Pacific Islander, includes codes 18-68 for areas that do
not report them separately
Blank — Not reported.
Beginning in 2003, some states started allowing multiple race responses for birth records. For
example, in 2010, multiple race was reported by California, Colorado, Delaware, District of
Columbia, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana (for births
occurring after November 30 2010), Maryland, Michigan, Missouri, Montana, Nebraska, Nevada,
New Hampshire, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon,
Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Washington, and
Wyoming, which used the 2003 revision of the U.S. Standard Certificate of Live Birth, as well as,
Hawaii, Mnnesota and Rhode Island , which used the 1989 revision of the U.S. Standard Certificate
of Live Birth. These 38 states and the District of Columbia accounted for 83 percent of U.S. births in
2010 and reported 2.1 percent of mothers as multiracial, with levels varying from less than 1%
(Indiana, New Hampshire, and Texas) to 35% (Hawaii). In order to provide uniformity and
comparability of data across the years, NVSS bridged the multiple-race data according to the
combination of races, Hispanic origin, sex, and age indicated on the birth certificate of the
mother or father to obtain a single race for each birth record reporting multiple races in the
NVSS datasets. For such records, the single race or bridged multiple race was given by the
variable MBRACE. MB RACE is given the following values:
MBRACE
01 White - single race
02 Black - single race
03 American Indian / Alaskan Native - single race
04 Asian Indian - single race
05 Chinese - single race
06 Filipino - single race
07 Japanese - single race
08 Korean - single race
09 Vietnamese - single race
10 Other Asian - single race
11 Hawaiian - single race
12 Guamanian - single race
13 Samoan - single race
14 Other Pacific Islander - single race
21 White - bridged multiple race
22 Black - bridged multiple race
23 American Indian / Alaskan Native - bridged multiple race
24 Asian / Pacific Islander - bridged multiple race
Blank - Not on certificate
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A new variable CRACE was created by combining the data from MRACE and MBRACE using
the following logic. CRACE is equal to MRACE if MRACE is not a missing value. Otherwise,
CRACE is equal to MBRACE.
The mother's Hispanic origin for 2003 is characterized by the variable UMHISP. UMHISP
assumes the following values:
UMHISP
0 ... Non-Hispanic
1 ... Mexican
2 ... Puerto Rican
3 ... Cuban
4 ... Central or South American
5 ... Other and unknown Hispanic
9 ... Origin unknown or not stated
Based on the above data, following categories of the mother's race/ethnicity were defined:
• White non-Hispanic (CRACE = 1 or 21 and UMHISP = 0);
• Black non-Hispanic (CRACE = 2 or 22 and UMHISP = 0);
• American Indian/Alaskan Native (AIAN) non-Hispanic (CRACE = 3 or 23 and
UMHISP =0);
• Asian or Pacific Islander (API) non-Hispanic (CRACE is 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 18, 24, 28, 38, 48, 58, 68, or 78 and UMHISP = 0);
• Hispanic Mexican American (UMHISP = 1);
• Hispanic Puerto Rican (UMHISP = 2);
• All Hispanic (UMHISP = 1, 2, 3, 4, or 5); and
• Unknown ethnicity (UMHISP = 9).
In approximately 0.5% of the birth certificate records, the mother's race was not stated. In those
cases, if the father's race was stated, then the father's race was used to impute the mother's race.
Otherwise, the mother's race was imputed from the mother's race on the preceding record with a
known mother's race. Thus, a mother's race was assigned to all the records.
Years 2004-2013
o Mother's Age: The mother's age for 2004-2013 is characterized by the variable MAGER.
This variable ranges from 12 - 50 and gives the age of mother in single years for ages 13
to 49, and codes the age group as 12 for ages 10 - 12 and as 50 for ages 50 and older. For
these analysis, the following age groups for the mother were defined:
• Mother's age less than 20 years (MAGER < 20);
• Mother's age between 20 and 39 (20 < MAGER < 40); and
• Mother's age is 40 or greater (MAGER > 40).
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o Mother's Race and Hispanic Origin: Just as for 2003, the mother's race and Hispanic
origin category are given by the variables MRACE or MBRACE, and UMHISP
respectively. The categories of the mother's race/ethnicity were defined exactly as for
2003.
In approximately 1% of the birth certificate records for 2004-2005, 2% of the birth certificate
records reporting single races in 2006-2010, 6-7% of the birth certificate records reporting
multiple races in 2006-2010, and 6% of the birth certificate records for 2011-2013, the mother's
race was not stated or reported as "other" race. In those cases, if the father's race was stated, then
the father's race was used to impute the mother's race. Otherwise, the mother's race was imputed
from the mother's race on the preceding record with a known mother's race; for 2006 and later,
the race for Hispanic mothers was imputed from the preceding record of a Hispanic mother with
a known race. Thus, a mother's race was assigned to all the records.
Years 2014-2019
o Mother's Age: The mother's age for 2014-2019 is characterized by the variable MAGER
This variable ranges from 12 - 50 and gives the age of mother in single years for ages 13
to 49, and codes the age group as 12 for ages 10 - 12 and as 50 for ages 50 and older. For
these analysis, the following age groups for the mother were defined:
• Mother's age less than 20 years (MAGER < 20);
• Mother's age between 20 and 39 (20 < MAGER < 40); and
• Mother's age is 40 or greater (MAGER > 40).
0 Mother's Race and Hispanic Origin: The mother's race and Hispanic origin category are
given by the variables MBRACE (redefined), and MHISPR respectively. The categories
of the mother's race/ethnicity were defined as follows:
MBRACE (single race or multiple races bridged to a single race)
01 White
02 Black
03 American Indian / Alaskan Native
04 Asian or Pacific Islander
UMHISP
0 ... Non-Hispanic
1 ... Mexican
2 ... Puerto Rican
3 ... Cuban
4 ... Central or South American
5 ... Other and unknown Hispanic origin
9 ... Hispanic origin not stated
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Based on the above data, following categories of the mother's race/ethnicity were defined:
• White non-Hispanic (MBRACE = 1 and MHISPR = 0);
• Black non-Hispanic (MBRACE = 2 and MHISP R = 0);
• American Indian/Alaskan Native (AIAN) non-Hispanic (MBRACE = 3 and
MHISPR = 0);
• Asian or Pacific Islander (API) non-Hispanic (MBRACE = 4 and MHISP R = 0);
• Hispanic Mexican American (MHISP R =1);
• Hispanic Puerto Rican (MHISP R = 2);
• All Hispanic (MHISP R = 1, 2, 3, 4, or 5); and
• Unknown ethnicity (MHISP R = 9).
In approximately 6-7% of the birth certificate records for 2014- 2019, the mother's race was not
stated or reported as "other" race. In those cases, if the father's race was stated, then the father's
race was used to impute the mother's race. Otherwise, the mother's race was imputed from the
mother's race on the preceding record with a known mother's race; for 2006 and later, the race
for Hispanic mothers was imputed from the preceding record of a Hispanic mother with a known
race. Thus, a mother's race was assigned to all the records.
Calculation of Indicator
For each demographic group, the percentage of preterm births was calculated as the number of
preterm births divided by the total number of births:
Percentage of preterm births =
Number of preterm births for mothers in group / Number of births with a stated gestation
period for mothers in group x 100%
For each demographic group, the percentage of term low birth weight births was calculated as
the number of term low birth weight births divided by the total number of births:
Percentage of term low birth weight births =
Number of low birth weight births at term for mothers in group / Number of births with a
stated gestation period and a stated birth weight for mothers in group x 100%
Questions and Comments
Questions regarding these methods, and suggestions to improve the description of the methods,
are welcome. Please use the "Contact Us" link at the bottom of any page in the America's
Children and the Environment website.
Statistical Comparisons
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Statistical analyses of the percentages of preterm or term low birth weight babies were used to
determine whether the differences between percentages for different demographic groups were
statistically significant. Using a logistic regression model, the logarithm of the odds that a given
baby is preterm or term low birth weight is assumed to be the sum of explanatory terms for the
mother's age group and/or race/ethnicity. The odds that a given baby is preterm is the probability
that the baby is preterm divided by the probability that the baby is not preterm (similarly for term
low birth weight). Thus, if two demographic groups have similar (or equal) percentages of
preterm or term low birth weight births, then they will also have similar (or equal) values for the
logarithm of the odds. Using this model, the difference in the percentage between different
demographic groups is statistically significant if the difference between the corresponding sums
of explanatory terms is statistically significantly different from zero. The uncertainties of the
regression coefficients were calculated using the SAS® (SAS Institute, Cary, North Carolina)
statistical software GENMOD procedure and a binomial logistic model, treating the births for
each demographic subgroup as a random sample of births. A p-value at or below 0.05 implies
that the difference is statistically significant at the 5% significance level. No adjustment is made
for multiple comparisons.
For these statistical analyses we used six race/ethnicity groups: White non-Hispanic; Black non-
Hispanic; Asian or Pacific Islander non-Hispanic; American Indian or Alaska Native non-
Hispanic; Hispanic; Unknown ethnicity. In addition, for specific comparisons between the
Mexican and Puerto Rican subgroups, we applied a similar statistical analysis to only the data
from Mexican or Puerto Rican births using two ethnicity groups: Mexican; Puerto Rican. We
also used three age groups: < 20, 20-39, and 40+.
For each type of comparison, we present unadjusted and adjusted analyses. The unadjusted
analyses directly compare a percentage between different demographic groups. The adjusted
analyses add other explanatory variables to the statistical model and use the statistical model to
account for the possible confounding effects of these other variables. For example, the
unadjusted race/ethnicity comparisons use and compare the percentages between different
race/ethnicity pairs. The adjusted analyses add age terms to the statistical model and compare the
percentages between different race/ethnicity pairs after accounting for the effects of the age
group. For example, if White non-Hispanics tend to be older when they have babies compared to
Black non-Hispanics, and if the probability of preterm births strongly depends on the mother's
age only, then the unadjusted differences between these two race/ethnicity groups would be
significant but the adjusted difference (taking into account age) would not be significant.
Comparisons of the percentages of preterm and term low birth weight births between pairs of
race/ethnicity groups in 2019 are shown in Table 1. For the unadjusted comparisons, the only
explanatory variables are terms for each race/ethnicity group. For these unadjusted comparisons,
the statistical tests compare the percentage for each pair of race/ethnicity groups. For the
adjusted comparisons ("Adjusted for age"), the explanatory variables are terms for each
race/ethnicity group together with terms for each age group. For these adjusted comparisons, the
statistical test compares the pair of race/ethnicity groups after accounting for any differences in
the age distributions between the race/ethnicity groups.
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Additional comparisons of the percentages of preterm and term low birth weight births are
shown in Table 2. The Against = "age" unadjusted p-value compares the percentages for
different age groups in 2019. The adjusted p-value includes adjustment terms for race/ethnicity
in the model. The Against = "year" p-value examines whether the linear trend in the percentages
is statistically significant; the adjusted model for trend adjusts for demographic changes in the
populations from year to year by including terms for age and race/ethnicity. The p-values for
Against = "year" and specific values of Subset examine whether the trend for that race/ethnicity
or age group demographic subset is statistically significant. The trend analyses are presented for
the trends 1993-2006 and 2007-2019. Since the estimated gestation period was based on the date
of the last menstrual period in 1993-2006 and was based on the obstetric/clinical estimate in
2007-2019, the trend 1993- 2019 was not evaluated. Overall trend analyses are presented for all
births, singleton births, and multiple births.
For more details on these statistical analyses, see the memorandum by Cohen (2011).1
1 Cohen, J. 2011. Selected statistical methods for testing for trends and comparing years or demographic groups in
other ACE health-based indicators. Memorandum submitted to Dan Axelrad, EPA, 16 June, 2011.
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Table 1. Statistical significance tests comparing the percentages of preterm or term low birth
weight births between pairs of race/ethnicity groups for 2019.
P-VALUES
Variable
First race/ethnicity
group
Second race/ethnicity
group
Unadjusted
Adjusted for
age
Preterm
White non-Hispanic
Black non-Hispanic
<0.001
<0.001
Preterm
White non-Hispanic
AIAN non-Hispanic
<0.001
<0.001
Preterm
White non-Hispanic
API non-Hispanic
<0.001
<0.001
Preterm
White non-Hispanic
Hispanic
<0.001
<0.001
Preterm
White non-Hispanic
Unknown ethnicity
<0.001
<0.001
Preterm
Black non-Hispanic
AIAN non-Hispanic
<0.001
<0.001
Preterm
Black non-Hispanic
API non-Hispanic
<0.001
<0.001
Preterm
Black non-Hispanic
Hispanic
<0.001
<0.001
Preterm
Black non-Hispanic
Unknown ethnicity
<0.001
<0.001
Preterm
AIAN non-Hispanic
API non-Hispanic
<0.001
<0.001
Preterm
AIAN non-Hispanic
Hispanic
<0.001
<0.001
Preterm
AIAN non-Hispanic
Unknown ethnicity
0.215
0.912
Preterm
API non-Hispanic
Hispanic
<0.001
<0.001
Preterm
API non-Hispanic
Unknown ethnicity
<0.001
<0.001
Preterm
Hispanic
Unknown ethnicity
<0.001
<0.001
Preterm
Mexican
Puerto Rican
<0.001
<0.001
Term low birth weight
White non-Hispanic
Black non-Hispanic
<0.001
<0.001
Term low birth weight
White non-Hispanic
AIAN non-Hispanic
<0.001
0.002
Term low birth weight
White non-Hispanic
API non-Hispanic
<0.001
<0.001
Term low birth weight
White non-Hispanic
Hispanic
<0.001
<0.001
Term low birth weight
White non-Hispanic
Unknown ethnicity
<0.001
<0.001
Term low birth weight
Black non-Hispanic
AIAN non-Hispanic
<0.001
<0.001
Term low birth weight
Black non-Hispanic
API non-Hispanic
<0.001
<0.001
Term low birth weight
Black non-Hispanic
Hispanic
<0.001
<0.001
Term low birth weight
Black non-Hispanic
Unknown ethnicity
<0.001
<0.001
Term low birth weight
AIAN non-Hispanic
API non-Hispanic
<0.001
<0.001
Term low birth weight
AIAN non-Hispanic
Hispanic
0.146
0.187
Term low birth weight
AIAN non-Hispanic
Unknown ethnicity
0.001
<0.001
Term low birth weight
API non-Hispanic
Hispanic
<0.001
<0.001
Term low birth weight
API non-Hispanic
Unknown ethnicity
<0.001
<0.001
Term low birth weight
Hispanic
Unknown ethnicity
<0.001
<0.001
Term low birth weight
Mexican
Puerto Rican
<0.001
<0.001
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Health: Adverse Birth Outcomes
Table 2. Other statistical significance tests comparing the percentage of preterm and term low
birth weight births.
P-VALUES
Variable
From
To
Against
Subset
Unadjusted
Adjusted*
Preterm
2019
2019
age
<0.001
<0.001
Preterm
2019
2019
race
<0.001
<0.001
Preterm
1993
2006
year
<0.001
<0.001
Preterm
1993
2006
year
White non-Hispanic
<0.001
<0.001
Preterm
1993
2006
year
Black non-Hispanic
0.010
0.001
Preterm
1993
2006
year
AIAN non-Hispanic
<0.001
<0.001
Preterm
1993
2006
year
API non-Hispanic
<0.001
<0.001
Preterm
1993
2006
year
Hispanic
<0.001
<0.001
Preterm
1993
2006
year
Unknown ethnicity
<0.001
<0.001
Preterm
1993
2006
year
<20
<0.001
<0.001
Preterm
1993
2006
year
20-39
<0.001
<0.001
Preterm
1993
2006
year
40+
<0.001
<0.001
Preterm
1993
2006
year
Singleton
<0.001
<0.001
Preterm
1993
2006
year
Multiple
<0.001
<0.001
Preterm
2007
2019
year
<0.001
<0.001
Preterm
2007
2019
year
White non-Hispanic
<0.001
<0.001
Preterm
2007
2019
year
Black non-Hispanic
<0.001
<0.001
Preterm
2007
2019
year
AIAN non-Hispanic
<0.001
<0.001
Preterm
2007
2019
year
API non-Hispanic
<0.001
<0.001
Preterm
2007
2019
year
Hispanic
<0.001
<0.001
Preterm
2007
2019
year
Unknown ethnicity
0.012
<0.001
Preterm
2007
2019
year
<20
<0.001
<0.001
Preterm
2007
2019
year
20-39
<0.001
<0.001
Preterm
2007
2019
year
40+
0.327
<0.001
Preterm
2007
2019
year
Singleton
<0.001
<0.001
Preterm
2007
2019
year
Multiple
<0.001
<0.001
Term low birth weight
2019
2019
age
<0.001
<0.001
Term low birth weight
2019
2019
race
<0.001
<0.001
Term low birth weight
1993
2006
year
<0.001
<0.001
Term low birth weight
1993
2006
year
White non-Hispanic
<0.001
<0.001
Term low birth weight
1993
2006
year
Black non-Hispanic
0.124
0.987
Term low birth weight
1993
2006
year
AIAN non-Hispanic
0.001
0.002
Term low birth weight
1993
2006
year
API non-Hispanic
<0.001
<0.001
Term low birth weight
1993
2006
year
Hispanic
<0.001
<0.001
Term low birth weight
1993
2006
year
Unknown ethnicity
0.992
0.917
Term low birth weight
1993
2006
year
<20
<0.001
<0.001
Term low birth weight
1993
2006
year
20-39
<0.001
<0.001
Term low birth weight
1993
2006
year
40+
<0.001
<0.001
Term low birth weight
1993
2006
year
Singleton
0.001
<0.001
Term low birth weight
1993
2006
year
Multiple
<0.001
<0.001
Term low birth weight
2007
2019
year
<0.001
<0.001
Term low birth weight
2007
2019
year
White non-Hispanic
<0.001
<0.001
Term low birth weight
2007
2019
year
Black non-Hispanic
<0.001
<0.001
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Health: Adverse Birth Outcomes
P-VALUES
Variable
From
To
Against
Subset
Unadjusted
Adjusted*
Term low birth weight
2007
2019
year
AIAN non-Hispanic
<0.001
<0.001
Term low birth weight
2007
2019
year
API non-Hispanic
<0.001
<0.001
Term low birth weight
2007
2019
year
Hispanic
<0.001
<0.001
Term low birth weight
2007
2019
year
Unknown ethnicity
0.638
0.706
Term low birth weight
2007
2019
year
<20
<0.001
<0.001
Term low birth weight
2007
2019
year
20-39
<0.001
<0.001
Term low birth weight
2007
2019
year
40+
0.801
0.030
Term low birth weight
2007
2019
year
Singleton
<0.001
<0.001
Term low birth weight
2007
2019
year
Multiple
<0.001
<0.001
*For Against = "age," the p-values are adjusted for race/ethnicity.
For Against = "year," the p-values are adjusted for age and race/ethnicity.
Data Files
The following files are needed to calculate this indicator.
Birth data:
• NATLXXXX.DAT.Z, where XXXX denotes the four-digit year for years 1993-2006.
Each file is a compressed file that when decompressed gives the national birth certificate
data for a calendar year for births in the 50 U.S. states and Washington DC. The
companion files with birth certificate data for U.S. territories were not used for these
analyses. These files together with SAS® code to extract and read these data files and
convert them into SAS® format were obtained from the National Bureau of Economic
Research (NBER) at the url:
http://www.nber.org/data/vital-statistics-natalitv-data.html
• NatlXXXXus.zip, where XXXX denotes the four-digit year for years 2007-2010. Each
file is a compressed file that when decompressed gives the national birth certificate data
for a calendar year for births in 50 U.S. states and Washington D.C. The SAS® code to
process 2006-year data was downloaded from NBER as described above and modified to
process the data contained in these files. These files were obtained from vital statistics
data maintained online by the Centers for Disease Control and Prevention and available
at the url:
http://www.cdc.gov/nchs/data access/Vitalstatsonline.htm
• natlXXXX.sas7bdat.zip, where XXXX denotes the four-digit year for years 2011-2018.
Each file is a compressed file that when decompressed gives a SAS® data set with the
national birth certificate data for a calendar year for births in 50 U.S. states and
Washington D.C. These files were created by NBER by processing the vital statistics data
maintained online by the Centers for Disease Control and Prevention. The files were
obtained from NBER at the url:
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Health: Adverse Birth Outcomes
http://www.nber.org/data/vital-statistics-natalitv-data.html
• birth_2019_nber_us.v2.sas7bdat. This file contains a SAS® data set with the national
birth certificate data for 2019 for births in 50 U.S. states and Washington D.C. This file
was created by NBER by processing the vital statistics data maintained online by the
Centers for Disease Control and Prevention. The file was obtained from NBER at the url:
http://www.nber.org/data/vital-statistics-natalitv-data.html
The variables needed for this indicator are the calendar year, mother's age, mother's race,
mother's ethnicity, length of gestation, plurality, and birth weight. The variable names and
formats vary by year and are detailed below.
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