Tobacco use during pregnancy
Information on smoking during pregnancy is reported on both the 1989 and the 2003 U.S.
Standard Certificates of Live Birth. The item was substantively modified for the 2003
certificate, however, and data based on the revised item are not comparable with those based on
the unrevised 1989 item. The revised 2003 question asks for the number of cigarettes smoked at
different intervals before and during the pregnancy. If the mother reports smoking in any of the
three trimesters of pregnancy she is classified as a smoker. In comparison, the unrevised 1989
item asks a “yes/no” question on tobacco use during pregnancy and the average number of
cigarettes per day with no specificity on timing during the pregnancy.
Data based on the 2003 revised item are available for all of 2008 for 24 states and Puerto
Rico. The 25 states are California, Colorado, Delaware, Idaho, Indiana, Iowa, Kansas,
Kentucky, Montana, Nebraska, New Hampshire, New Mexico, New York, North Dakota, Ohio,
Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Vermont, Washington,
and Wyoming. The tobacco use item for Florida, which implemented the revised birth certificate
as of January 1, 2004, and for Michigan, which had fully implemented the revised certificate as
of January 1, 2008, do not follow the standard format. As a result, tobacco use data for Florida
and Michigan are not comparable with either the 2003 revised or 1989 unrevised data (see
below) and are not included in the 2008 data files . Reliable data on tobacco use were not
available for Georgia for 2008.
Revised data on tobacco are not included in “Births: Final Data for 2008” . These data
are shown in Documentation Table 2. Revised and/or unrevised data on tobacco use are
presented in previous reports [35-38]. For 2003-2008 data based on the unrevised reporting area,
see VitalStats, and the public use data files [2,3].
Pregnancy risk factors
Both the 2003 and 1989 standard birth certificates collect pregnancy risk information in a
checkbox format. Ten risk factors are separately identified on the revised 2003 certificate
(Figure 1). Four of these risk factors; diabetes, pre-pregnancy hypertension, gestational
hypertension, and eclampsia are comparable across revisions, see Table D . Data for 2008 on
comparable risk factors are shown in Table I-6, available at
http://www.cdc.gov/nchs/data/nvsr/nvsr59/nvsr59_01_tables.pdf. Selected risk factors new to
the revised certificate were presented in a report based on 2006 data ; 2007 data are
presented in Table R-1 of the 2007 User Guide ; 2008 data will be presented in an upcoming
report and are available in Documentation Table 3.
Both the revised and unrevised formats allow for the reporting of more than one risk
factor and include a choice of “None” (or “None of the above” in the case of the revised
certificate). Accordingly, if the item is not completed, it is classified as not stated. Levels of
reporting completeness by state for pregnancy risk factors are shown in Table B.
For detailed instructions and definitions for the pregnancy risk factors included on the
revised 2003 certificate see: Guide to Completing the Facility Worksheets for the Certificate of
Live Birth and Report of Fetal Death (2003 Revision) . Definitions for the 1989 certificate
items are also available .
Diabetes during pregnancy – The 2003 revision splits reporting of diabetes during
pregnancy into prepregnancy (diagnosed prior to this pregnancy) and gestational (diagnosed in
this pregnancy) diabetes. In comparison, the 1989 certificate captures information on maternal
diabetes as a single item only. This change, along with more general enhancements to the
collection of data under the 2003 revision, appears to have improved reporting of diabetes during
pregnancy in states adopting the 2003 certificate. Improved reporting of this item as states
implemented the 2003 revised birth certificate contributed to the national increase between 2003
and 2008 (see Tables 18 and 19 of “Births: Final Data for 2008” and Table I-6 for 2008 rates
) ; diabetes rates rose by more than 1/3, on average, as states implemented the 2003
certificate revision, compared with less than 7 percent annual increases for unrevised states and
for revised states that had used the revised certificate for two or more years. This rise in diabetes
may also be the result of increased attention paid to diabetes by the medical community as well
as an actual increase in the occurrence of diabetes.
Information on the timing of prenatal care is available for both the 2003 revised and 1989
unrevised Certificates of Live Birth. However, the 2003 revision introduced substantive changes
in item wording and also to the sources of prenatal information. The wording of the prenatal
care item was modified to “Date of first prenatal visit” from “Month prenatal care began.” In
addition, the 2003 revision process resulted in recommendations that the prenatal care
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information be gathered from the prenatal care or medical records, whereas the 1989 revision did
not include a recommended source for these data. Accordingly, prenatal care data for the two
revisions are not directly comparable and are shown separately in tabulations and in the data file.
Revised data on prenatal care are not included in “Births: Final Data for 2008” .
These data are shown in Documentation Table 2. Revised and/or unrevised data on prenatal
care are presented in previous reports [35-38]. For 2003-2008 data based on the unrevised
reporting area, see VitalStats, and the public use data files [2,3].
Levels of utilization of prenatal care based on revised data are substantially lower than
those based on unrevised data. For the first year revised certificates are implemented, the
percentage of women reported to begin care in the first trimester typically falls in a state by at
least 10 percentage points . For example, unrevised 2007 data for Montana indicated that 84.0
percent of residents began care in the first trimester of pregnancy. This compares with a level of
73.4 percent for 2008 based on Montana revised data. Much, if not all of the difference between
2007 and 2008 for Montana and other revised states, is related to changes in reporting and not to
changes in prenatal care utilization.
Both the 2003 and the 1989 Standard Certificates of Live Birth collect information on
obstetric procedures in a checkbox format (Figures 1). Three procedures are separately
identified on the revised 2003 certificate: cervical cerclage, tocolysis, and external cephalic
version (successful or failed). Two procedures, induction of labor (captured under the
“Characteristics of labor and delivery” section of the revised 2003 certificate) and tocolysis are
comparable across revisions , see Table D. Data for 2008 on comparable obstetric procedures
are shown in Table I-6, available at
Obstetric procedures new to
the revised certificate were presented in a report based on 2006 data ; 2007 data are
presented in Table R-2 of the 2007 User Guide ; 2008 data will be presented in an upcoming
report and are available in Documentation Table 4.
Both the revised and unrevised certificate formats allow for the reporting of more than
one procedure and include a choice of “None” (or “None of the above” in the case of the revised
certificate). Accordingly, if the item is not completed, it is classified as “not stated.” Reporting
completeness for obstetric procedures by state is shown in Table B.
Due to inaccurate reporting in Georgia, Michigan, and Ohio, rates of successful external
cephalic version (ECV) are inflated and levels of failed ECV are underreported for these states.
As a result, overall levels of successful ECV for the revised reporting area are somewhat inflated
and overall levels of failed ECV are underestimated. Data for these items should be used with
caution. See the section on “State specific data quality issues” below for more information.
Detailed instructions and definitions for the obstetric procedures based on the revised
2003 certificate are presented in the Guide to Completing the Facility Worksheets for the
Certificate of Live Birth and Report of Fetal Death (2003 Revision) . Definitions for the
1989 certificate items are also available .
Characteristics of labor and delivery
Both the 2003 and the 1989 standard birth certificates collect characteristics of labor and
delivery in a checkbox format (Figures 1). The 2003 Standard Certificate of Live Birth includes
nine specific characteristics of labor and delivery. Three of these characteristics, Meconium,
Breech/malpresentation (collected under the “Method of delivery” item on the 2003 Certificate),
and Precipitous labor (collected under “Onset of labor” on the 2003 certificate) are comparable
across revisions , see Table D. Data for 2008 on comparable characteristics of labor and
delivery are shown in Table I-6, available at
Characteristics of labor and
delivery new to the revised certificate were presented in a report based on 2006 data ; 2007
data are presented in Table R-3 of the 2007 User Guide ; 2008 data will be presented in an
upcoming report and are available in Documentation Table 5.
Both the revised and unrevised certificate formats allow for the reporting of more than
one characteristic and include a choice of “None” (or “None of the above” in the case of the
revised certificate). If the item is not completed, it is classified as “not stated.” The percent of
records for which characteristics of labor and delivery items were not stated is shown in Table
The 1989 revision of the U.S. Standard Certificate of live birth (unrevised) provides a
single checkbox for “Breech/Malpresentation” under Complications of Labor and Delivery. On
the 2003 revision of the birth certificate (revised), this information is collected as two separate
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checkboxes: “Breech” and “Other” in the Fetal Presentation subsection of Method and Delivery.
Although by definition, the revised “Breech” and “Other” items combined are comparable to the
unrevised item, levels for revised states tend to be higher in general than those for non-revised
states. As a result, increases in the national “Breech/Malpresentation” rates observed since 2003
(the first year states began implementing the revised birth certificates) is likely largely a
reporting artifact; trends in Breech/Malpresentation rates and comparisons of rates among
revised and unrevised States should be viewed with caution.
The 2003 U.S. Standard Certificate of Live Birth includes the checkbox “non-vertex
presentation” under the category Characteristics of Labor and Delivery. Non-vertex presentation
is defined as any presentation other than vertex (i.e., any presentation other than the upper or
back part of the baby’s head) . Also included on the 2003 certificate under the category
“Method of Delivery—Final presentation at birth,” are the checkboxes “breech” and “other”
(noncephalic) presentation. Although “breech” and “other” presentations in the Method of
Delivery category are subsets of “non-vertex presentation,” the combined level of “breech” and
“other” presentations was higher than that for “non-vertex presentation” in Characteristics of
Labor and Delivery for 2008 (6.6 percent compared with 1.4 percent, respectively).
Furthermore, 68.6 percent of breech and 94.6 percent of other presentations were not classified
as nonvertex, suggesting that non-vertex presentation may be underreported.
Detailed instructions and definitions for the characteristics of labor and delivery collected
on the revised 2003 certificate are presented in the Guide to Completing the Facility Worksheets
for the Certificate of Live Birth and Report of Fetal Death (2003 Revision) . Definitions for
the 1989 certificate items are also available .
Place of delivery and attendant at birth
Both the 1989 and 2003 revisions of the U.S. Standard Certificate of Live Birth include
separate categories for hospitals, freestanding birthing centers, residence, and clinic or doctor's
office as the place of birth. In addition, the 2003 certificate queries whether the home birth was
planned to be a home delivery.
For both the revised and unrevised certificates, the four professional categories of
attendants are medical doctors, doctors of osteopathy, certified nurse midwives, and other
midwives. There is evidence that the number of live births attended by certified nurse midwives
[CNM] is understated , largely due to difficulty in correctly identifying the birth attendant
when more than one provider is present at the birth. (Anecdotal evidence suggests that some
hospitals require that a physician be reported as the attendant even where no physician is
physically present at midwife-attended births.)
Additional information on births occurring outside of hospitals, and on birth attendants,
can be found in “Technical appendix. Vital statistics of the United States: 1999, vol I, natality
Method of delivery
Several rates are computed for “Method of delivery.” The overall cesarean delivery rate
or total cesarean rate is computed as the percent of all births delivered by cesarean. The primary
cesarean rate relates the number of women having a first cesarean delivery to all women giving
birth who have never had a cesarean delivery. The denominator for the primary cesarean rate
includes the sum of primary cesareans and vaginal births without previous cesarean. The rate of
vaginal birth after previous cesarean (VBAC) delivery is computed by relating all VBAC
deliveries to the sum of VBAC and repeat cesarean deliveries, that is, to women with a previous
Information on method of delivery is reported on both the 2003 and 1989 Standard
Certificates of Live Birth. However, the format and wording of the method of delivery item on
the revised certificate differs from that of the unrevised certificate. The unrevised item asks a
direct question on whether the birth was vaginal, VBAC or a primary or repeat cesarean delivery.
In contrast, the revised method of delivery item asks if the final route of delivery was a vaginal
(with or without forceps or vacuum assistance) or a cesarean delivery. Information on the type
of vaginal (vaginal or VBAC) or type of cesarean delivery (primary or repeat) is calculated from
the response to a question under a different item, “Risk factors in this pregnancy” which asks if
the mother had a previous cesarean delivery.
As a result of these changes, although data on total cesarean deliveries appear to be very
comparable between revisions, information on type of vaginal or cesarean delivery is not. Rates
based on data from the revised certificates are substantially higher for VBACs and primary
cesareans, and lower for repeat cesareans, than rates based on data from unrevised certificates
. Accordingly, data on VBAC, primary, and repeat cesarean deliveries are not directly
comparable between revisions, and beginning with the 2005 data year, are presented separately
in tabulations  and in the data file.
Information on forceps and vacuum delivery is also available from both the 2003 revised
and 1989 unrevised birth certificates; these data appear to be comparable between revisions. The
2003 revision item was also expanded to include questions on whether attempted forceps or
vacuum deliveries were successful, and whether a trial of labor was attempted prior to cesarean
delivery. Method of delivery items new to the revised certificate were presented in a report
based on 2006 data ; 2007 data are presented in Table R-5 of the 2007 User Guide ; 2008
data will be presented in an upcoming report and are available in Documentation Table 6.
The primary measure used to determine the gestational age of the newborn is the interval
between the first day of the mother’s last normal menstrual period (LMP) and the date of birth.
The LMP is used as the initial date because it can be more accurately determined than the date of
conception, which usually occurs 2 weeks after the LMP. LMP measurement is subject to error
for several reasons, including imperfect maternal recall or misidentification of the LMP because
of post-conception bleeding, delayed ovulation, or intervening early miscarriage.
Births occurring before 37 completed weeks of gestation are considered to be preterm for
purposes of classification. At 37–41 weeks gestation, births are considered to be term, and at 42
completed weeks and over, post-term. These distinctions are consistent with the ICD–9 and
ICD–10  definitions. NCHS further categorizes births at less than 34 weeks as early preterm
and births at 34-36 weeks as late preterm. Beginning with “Births: Final data for 2008” ,
NCHS has also begun differentiating between early term (37-38 weeks) and full term (39-41
Before 1981, the period of gestation was computed only when there was a valid month,
day, and year of LMP. However, length of gestation could not be determined for a substantial
number of live-birth certificates each year because the day of LMP was missing. Beginning in
1981, weeks of gestation have been imputed for records with missing day of LMP when there is
a valid month and year. The imputation procedure and its effect on the data are described
elsewhere [11,50]. Reporting problems for this item persist and may occur more frequently
among some subpopulations, such as selected maternal race groups, and among births with
shorter gestations [43,51,52].
The 1989 revision of the U.S. Standard Certificate of Live Birth includes an additional
measure of gestational age, the item “Clinical estimate of gestation.” The comparable item on
the 2003 revision of the birth certificate is the “Obstetric estimate of gestation” – see definitions
. The clinical or obstetric estimate is compared with the length of gestation computed from
the LMP date when the latter appears to be inconsistent with birthweight. This is done for
normal weight births of apparently short gestations and very low birthweight births reported to
be full term. The procedures are described in NCHS instruction manuals [44,45].
The period of gestation for 6.2 percent of the births in 2008 was based on the clinical or
obstetric estimate of gestation. For 98 percent of these records, the clinical or obstetric estimate
was used because the LMP date was not reported. For the remaining 2 percent, the clinical or
obstetric estimate was used because it was compatible with the reported birthweight, whereas the
LMP-based gestation was not. In cases where the reported birthweight was inconsistent with
both the LMP-computed gestation and the clinical/obstetric estimate of gestation, the LMP-
computed gestation was used and birthweight was reclassified as "not stated." This was
necessary for 402 births or 0.01 percent of all birth records in 2008. The levels of the
adjustments were similar to those for earlier years. Despite these edits, substantial incongruities
in these data persist.
Birthweight is reported in some areas in pounds and ounces rather than in grams.
However, the metric system is used to tabulate and present the statistics to facilitate comparison
with data published by other groups. The categories for birthweight are consistent with the
recommendations in the International Classification of Diseases, Ninth Revision (ICD–9) and the
International Classification of Diseases, Tenth Revision (ICD–10) . The categories in gram
intervals and their equivalents in pounds and ounces are as follows:
Less than 500 grams = 1 lb 1 oz or less
500–999 grams = 1 lb 2 oz–2 lb 3 oz
1,000–1,499 grams = 2 lb 4 oz–3 lb 4 oz
1,500–1,999 grams = 3 lb 5 oz–4 lb 6 oz
2,000–2,499 grams = 4 lb 7 oz–5 lb 8 oz
2,500–2,999 grams = 5 lb 9 oz–6 lb 9 oz
3,000–3,499 grams = 6 lb 10 oz–7 lb 11 oz
3,500–3,999 grams = 7 lb 12 oz–8 lb 13 oz
4,000–4,499 grams = 8 lb l4 oz–9 lb l4 oz
4,500–4,999 grams = 9 lb 15 oz–11 lb 0 oz
5,000 grams or more = 11 lb l oz or more
ICD–9 and ICD–10 define low birthweight as less than 2,500 grams. This is a shift of 1
gram from the previous criterion of 2,500 grams or less, which was recommended by the
American Academy of Pediatrics in 1935 and adopted in 1948 by the World Health Organization
in the International Lists of Diseases and Causes of Death, Sixth Revision . Very low
birthweight is defined as less than 1,500 grams.
To establish the continuity of class intervals needed to convert pounds and ounces to
grams, the end points of these intervals are assumed to be half an ounce less at the lower end and
half an ounce more at the upper end. For example, 2 lb 4 oz–3 lb 4 oz is interpreted as 2 lb 3 ½
oz–3 lb 4 ½ oz. Births for which birthweights are not reported are excluded from the
computation of percentages.
The Apgar score is a measure of the need for resuscitation and a predictor of the infant's
chances of surviving the first year of life. It is a summary measure of the infant's condition
based on heart rate, respiratory effort, muscle tone, reflex irritability, and color. Each of these
factors is given a score of 0, 1, or 2; the sum of these 5 values is the Apgar score, which ranges
from 0 to 10. A score of 0 to 3 indicates an infant in need of resuscitation; a score of 4 to 6 is
considered intermediate; a score of 7 or greater indicates that the neonate is in good to excellent
The 1– and 5–minute Apgar scores were added to the U.S. Standard Certificate of Live
Birth in 1978 to evaluate the condition of the newborn infant at 1 and 5 minutes after birth. In
1995, NCHS discontinued collecting data on the 1-minute score. The 2003 revised certificate
includes the five minute score and also asks for a 10 minute score if the 5 minute score is less
than 6. The 2008 natality file includes information on the 5 minute score only. Data for 2008
for Apgar score are shown in Tables 18 and 19 in “Births: Final data for 2008” .
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