March of Dimes March of Dimes Peristats

Calculations

Overview

PeriStats is a database-driven Web site that aggregates data from multiple government agencies and organizations, including:

  • National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC)
  • National Center for Chronic Disease Prevention and Health Promotion, CDC
  • National Center for HIV, STD, and TB Prevention, CDC
  • Centers for Medicare and Medicaid Services (CMS), Department of Health and Human Services (DHHS)
  • Health Resources Services Administration (HRSA), DHHS
  • Substance Abuse and Mental Health Services Administration (SAMHSA)
  • U.S. Census Bureau
  • National Governors Association (NGA)
  • United States Department of Agriculture (USDA)
  • Agency for Healthcare Research and Quality (AHRQ)
  • March of Dimes

A primary goal of the web site is to present health indicators that are comparable across the entire United States, and when possible to show these indicators at the state, county and city level. The majority of the health indicators on PeriStats are calculated by the March of Dimes Perinatal Data Center using data obtained electronically from the source agency. Those data not calculated directly by the Perinatal Data Center are obtained directly from the source agency or their publications.

Perinatal Data Center Calculations

Calculations performed by the Perinatal Data Center generally follow the guidelines provided by the National Center for Health Statistics (NCHS).


Rates

Rates calculated by the Perinatal Data Center are processed using a series of programs written in SPSS software. All US total rates are based on the 50 states and the District of Columbia. Some rates are presented as aggregates for a combination of years (e.g. 2005-2008). Due to insufficient numbers some rates can not be shown on PeriStats. When rates for single years can not be shown, three-year aggregates are shown if available. If the three-year aggregates are not sufficient, that indicator will not be provided in order to ensure confidentialty..

When an item on a birth or death certificate is illegible or missing, it is coded by NCHS as "not stated" or "unknown." Denominators used in rates and ratios on PeriStats exclude values not stated.


Maternal Race/Ethnicity and Age

Many indicators are shown by race, race/ethnicity, and maternal age. Data provided by race and race/ethnicity reflect the race and ethnicity of the mother as indicated on the birth certificate. Race categories shown on PeriStats include: White, Black, Native American, and Asian, consistent with those reported by NCHS. Race/Ethnicity categories include: non-Hispanic white, non-Hispanic black, non-Hispanic Native American, non-Hispanic Asian/Pacific Islander and Hispanic. Race and ethnicity are reported separately on the birth certificate. When race of the mother is missing from the birth certificate, NCHS imputes race using race of the father, if available, or by assigning the specific race of the mother on the preceding record with a known race of mother (5.3% of live births in 2008).

While some states report the mother's age directly, most states do not, and maternal age is calculated by NCHS using the difference between the mother's and infant's dates of birth as reported on the birth certificate. From 1964 to 1996, births reported to occur to mothers younger than age 10 or older than age 49 years had age imputed according to the age of mother from the previous record with the same race and total birth order. After 1997, this range changed to mothers reported to be younger than age 9 or older than age 55. For records where age of mother was not reported, maternal age was imputed as described (0.01% of live births in 2008).


State Departments of Health

While one strength of PeriStats is the ability to make comparisons between States/local areas or between any state/local area and the U.S., the Web site is only a starting point for obtaining state and local data. We encourage users to work with their state health departments to analyze data in order to gain a deeper understanding of maternal and infant health issues specific to their area. Web site links for all state health departments are available on PeriStats.

Data provided on PeriStats may differ from rates obtained by state health departments and vital statistics agencies. This could be due to multiple causes. As part of the Vital Statistics Cooperative Program, states are required to send the National Center for Health Statistics (NCHS) natality and mortality data for a given year by a specific date. Sometimes states receive data after this date, which may result in slight differences in the rates calculated using NCHS processed data and state-processed data. Another reason rates may differ could be differences in the way NCHS and the States calculate variables and impute missing data.



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Binge Alcohol Use

Binge alcohol use among women of childbearing age is derived from the Behavioral Risk Factor Surveillance Survey (BRFSS), which is a health survey conducted by 50 states, 3 territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Alcohol use is part of a rotating core of questions asked every other year.

Methodological changes to the BRFSS in 2011 have affected the trends in prevalence estimates and they are not comparable to earlier years. The changes include the addition of cellular phones and improvements in the statistical weighting methods. More info can be found on the CDC Web site.

The calculation for the BRFSS binge drinking indicator is performed by the March of Dimes Perinatal Data Center, and includes the percent of women of childbearing age (18-44 years) who engage in binge alcohol use. Binge alcohol use is defined as having five or more drinks on at least one occasion during the past month. Beginning in 2006, binge alcohol use is defined as having four or more drinks on at least one occasion during the past month. Prior to 2006, binge alcohol use is defined as having five or more drinks on at least one occasion during the past month. US rate is the median of states which reported that year. More background can be found at the BRFSS Web site.

Birth Rates and Percentage of Births

Birth Rates are the number of live births per 1,000 persons in a specified group. Birth rates on PeriStats are calculated as the number of live births per 1,000 women 15-44 years of age, often referred to as a fertility rate. The denominator for this calculation is based on population data from the U.S. Census Bureau, available through the National Center for Health Statistics Web site. For more information, see calculation notes on Population.

Percentage of births calculations show the distribution of live births by race, race/ethnicity, and maternal age. Calculations are based on the number of live births in a specified group divided by all live births, multiplied by 100. Data for distributions by race and maternal age sum to 100 percent. Distributions by race/ethnicity do not sum to 100% due to live births missing data on ethnicity.

Birthweight

Birthweight rates are stratified into three categories: very low birthweight (less than 1500 grams or 3 1/3 pounds), low birthweight (less than 2500 grams or 5 1/2 pounds, includes very low birthweight) and not low birthweight (2500 grams or greater). Calculations are based on the number of live births to infants in a specific birthweight category divided by all live births, less the not-stated values multiplied by 100. Low birthweight and very low birthweight rates among singletons and multiples are calculated the same way.

Delivery Method

Note: In 2003 states started to implement the 2003 revision of the U.S. Standard Certificate of Live Birth. Comparisons of some method of delivery data should be made with caution. See detailed description below.


Calculation

Delivery Method rates are calculated for total cesarean sections, primary cesarean sections, vaginal births after cesarean sections (VBAC), and repeat cesarean sections.

The total cesarean section rate is calculated as the number of births delivered by cesarean section divided by the total number of live births less the not-stated values for delivery method, multiplied by 100.

The primary cesarean section rate is calculated as the number of women having a first cesarean delivery divided by the number of live births to women who have never had a cesarean delivery, multiplied by 100. The denominator for this rate excludes those with method of delivery classified as repeat cesarean, vaginal birth after previous cesarean, or method not stated.

The VBAC rate is calculated as the number of VBAC deliveries resulting in a live birth divided by the sum of VBAC and repeat cesarean deliveries, multiplied by 100.

The repeat cesarean section rate is calculated as the number of repeat cesarean deliveries resulting in a live birth divided by the sum of VBAC and repeat cesarean deliveries, multiplied by 100.


Impact of Birth Certificate Revision

The transition from the 1989 revision of the U.S. Standard Certificate of Live Birth to the 2003 revision has some implications on tracking rates of primary and repeat cesarean sections and VBAC deliveries in the United States.(1) The method of delivery item on the 2003 revision specifically asks if the mother had a previous cesarean section delivery under the "Risk Factors for Pregnancy" section of the birth certificate. In past revisions this information was indicated by a checkbox for VBAC under the method of delivery section. As a result of this modification, rates of VBAC and primary cesarean delivery from the 2003 revision are not comparable to data collected using earlier birth certificate revisions. Specifically, under the 2003 revision, rates of VBAC deliveries and primary cesarean section deliveries are slightly higher than expected, and repeat cesarean section deliveries (not shown on the PeriStats web site) are slightly lower. Total cesarean section and vaginal delivery rates are not impacted.

The state implementation of the 2003 revision also impacts U.S. and state temporal trends. While some states began using the revised birth certificate in 2003, the schedule for implementation varies by state. Therefore, starting in 2003, total U.S. rates of VBAC and primary cesarean deliveries are not reported due to data incompatibilities between states. Furthermore, some states have implemented the 2003 revision mid-year, and in these cases data for that year are not shown. In 2007 not all births in Michigan are reported based on the 2003 revision, and data are not shown for that year. Additionally, New York state started using the 2003 revised birth certificate in 2004 and New York City implemented in 2008. New York state VBAC and primary cesarean delivery rates exclude New York City from 2004 to 2007. Data for New York City can be found separately under city/county data.

On the PeriStats web site, graph bars displaying VBAC and primary cesarean delivery data based on the 2003 revision are shown in red instead of the standard blue color. Tables indicate the change with an asterisk (*). At the U.S. level VBAC and primary cesarean delivery rates for the total revised states are provided below the graph for the most recent year available. In addition, the functionality that allows you to make comparisons between regions has been removed from the VBAC and primary cesarean delivery section of the web site. To date the following states on the PeriStats web site have implemented the 2003 revision:

  • 2003: PA, WA
  • 2004: FL (mid-year), ID, KY, NH (mid-year), NY (excluding New York City), SC, TN
  • 2005: KS, NE, PR, TX, VT (mid-year)
  • 2006: CA (partially), DE, ND, OH, SD, WY
  • 2007: CO, GA (mid-year), IN, IA, MI (partially)
  • 2008: MT, NM, New York City, OR
  • 2009: DC (mid-year), NV (mid-year), OK (mid-year), PR, UT
  • 2010: IL, LA (mid-year), MD, MO, NC (mid-year)
  • 2011: MA (mid-year), MN (mid-year), WI

Beginning with the 2011 data year, the National Center for Health Statistics no longer includes unrevised data for primary and repeat cesarean sections and VBAC on the data file.

This section of the web site will be updated as additional states implement the 2003 U.S. Standard Certificate of Live Birth.

  1. Martin JA, Hamilton BE, Sutton PD, et al. Births: Final data for 2003. National vital statistics reports; vol 54 no 2. Hyattsville, MD: National Center for Health Statistics. 2005.

Federal Poverty Level

The percent of women (15-44 years) and children (<19 years) below the federal poverty level is obtained from the U.S. Census Bureau. Data is collected by the Census using the Current Population Survey (CPS), a monthly survey of about 50,000 households. The sample is selected to represent the civilian non-institutional population. More background can be found at the CPS Web site.

Fetal and Perinatal Mortality Rates

Fetal death is defined as death prior to delivery of fetus, and which is not an induced termination of pregnancy. In PeriStats, data are presented for "late fetal deaths" and include those with a stated period of gestation 28 weeks or more. Late fetal mortality rates are computed as the number of fetal deaths at 28 weeks of gestation or more divided by the number of live births and fetal death at 28 weeks or more, multiplied by 1,000.

Perinatal death refers to one around the time of delivery. In PeriStats, perinatal mortality includes infant deaths less than 7 days of age and late fetal deaths at 28 weeks of gestation or more. Perinatal mortality rates are calculated as the number of infant deaths and fetal deaths divided by the number of live births and fetal deaths.

The number of live births plus fetal deaths in the specified gestational age group in the denominators for fetal and perinatal mortality rates represents the population at risk of a fetal and perinatal death. For late fetal mortality rates, the numerator is calculated using data from the Fetal Death Data File from NCHS, and the denominator is calculated using data from the Final Natality File from NCHS for the number of live births and the Fetal Death Data File for the number of fetal deaths at 28 weeks gestation or more. For perinatal mortality rates, the numerator is calculated using data from Fetal Death Data File from NCHS and numerator file in Period Linked Birth/Infant Death Data Set, and the denominator is calculated using the Fetal Death Data file from NCHS and the Live Birth Denominator File in Period Linked Birth/infant Death Data Set that accompanies the numerator file.

Reporting requirement for fetal death data

Reporting requirements for fetal deaths vary by state and these differences have important implications for comparisons of fetal and perinatal mortality rates by state. (1) The majority of states require reporting of fetal deaths of 20 weeks of gestation or more, or a minimum of 350 grams birthweight or some combination of the two. More information about state reporting requirements can be found in Fetal and Perinatal Mortality, United States (National Vital Statistic Reports, NCHS). PeriStats presents late fetal mortality rates in order to account for these differences and provide more comparable data across states.

Fetal and Perinatal Mortality by Maternal Race/Ethnicity

Before 2005, Oklahoma did not report Hispanic origin of mother. Therefore, 2002-2004 and 2003-2005 averages of US, region and HHS region for late fetal and perinatal mortality rates by race/ethnicity exclude Oklahoma.

City-Level Fetal and Perinatal Mortality Rates>

Due to issues in reporting, fetal and perinatal mortality rates for Albuquerque, New Mexico and Tulsa, Oklahoma are not available on PeriStats.

The 2003 Revision of the U.S. Standard Report of Fetal Death

Because the variables included in the PeriStats are comparable between the 1998 and 2003 revisions, the state implementation of the 2003 revision has little or no effect on the data. (1) To date the following states on the PeriStats web site have implemented the 2003 revision:

  • 2003: MI(partially), WA
  • 2004: ID, UT, KY(mid-year), OK(mid-year)
  • 2005: KS, MD, NE, NH, SD

This section of the web site will be updated as additional states implement the 2003 U.S. Standard Certificate of Death.

1. MacDorman MF, Hoyert DL, Martin JA, Munson ML, Hamilton BE. Fetal and Perinatal Mortality, United States, 2003. National vital statistics reports; vol 55 no 6. Hyattsville, MD: National Center for Health Statistics. 2007.

Folic Acid

Folic acid-related data include results from the March of Dimes National Survey of Pre-Pregnancy Awareness and Behavior. The survey is conducted by Gallup and funded by the CDC. This telephone survey was conducted in 1995, 1997, 1998, 2000-2005, 2007, and 2008 using a nationally representative sample targeting approximately 2,000 English-speaking women ages 18-45 each year. The margin of error is +/- 3%.

Illicit Drug Use

Illicit drug use among population ages 12 and older is derived from the National Survey on Drug Use & Health (NSDUH), which is the primary source of statistical information on the use of illegal drugs by the U.S. population. The survey is sponsored by the Substance Abuse and Mental Health Services Administration (SAMHSA). The NSDUH collects information from residents of households, non-institutional group quarters (e.g., shelters, rooming houses, dormitories), and civilians living on military bases. Persons excluded from the survey include homeless persons who do not use shelters, active military personnel, and residents of institutional group quarters, such as jails and hospitals.

A small subset of data from NSDUH is available on PeriStats, and includes the percent of the population ages 12 and older that engage in illicit drug use. To ensure reliability, data are provided for a 2-year combined period. Illicit drug use indicates past month use at least once of marijuana/hashish, cocaine (including crack), inhalants, hallucinogens (including PCP and LSD), heroin, or any prescription-type psychotherapeutic used non-medically. More background is available at the NSDUH Web site.

Infant Mortality

Infant Mortality Rates

Infant mortality rates are calculated as the number of deaths in the first year of life divided by the number of live births, multiplied by 1000. For the years 1990-1994, the numerator is calculated using data from the Final Mortality File from NCHS, and the denominator is calculated using data from the Natality File. For the years after 1994, the numerator is calculated using data from the Period Linked Birth/Infant Death File, and the denominator is calculated using the Live Birth Denominator File that accompanies the numerator file. The period linked birth/infant death file links information from the birth certificate for each infant under 1 year of age who died in the 50 States, the District of Columbia, Puerto Rico, the Virgin Islands, or Guam and allows more detailed analysis of infant mortality patterns. This file was not prepared by NCHS for the years 1990-1994.

Age at Infant Death

Age at infant death rates include calculations for two age-specific categories: neonatal deaths and postneonatal deaths. The neonatal death rate is calculated as the number of infant deaths that occur between 0-27 days of life (often referred to as the 1st month of life) divided by the number of live births, multiplied by 1000. The postneonatal death rate is calculated as the number of infant deaths that occur from 28 days to under 1 year of life, divided by the number of live births, multiplied by 1000.

Cause of Infant Death

Cause of Infant Death rates are calculated using the Period Linked Birth/Infant Death File for the following causes of death: birth defects, prematurity/low birthweight, sudden infant death syndrome, respiratory distress syndrome, maternal complications of pregnancy, and neural tube defects. Rates are calculated as the number of cause-specific infant deaths divided by the number of live births, multiplied by 100,000.

All causes of death are based solely on the underlying cause of death and compiled in accordance with the International Statistical Classifications of Diseases and Related Health Problems - Ninth Revision (ICD-9) for 1995 through 1998, and Tenth Revision (ICD-10) beginning in 1999. When comparing data between these time periods, it is important to consider the potential impact on coding and definitions of cause of death categories that may have occurred upon transitioning from ICD-9 to ICD-10. To compensate for these discontinuities, NCHS has published cause-specific comparability ratios that when applied more clearly represent trends in mortality statistics from 1998 to 1999. Comparability ratios have not been applied in PeriStats.


Cause of Death ICD-9 Codes ICD-10 Codes
Birth Defects P07 765
Prematurity/LBW Q00-Q99 740-759
Sudden infant death syndrome R95 798.0
Respiratory distress syndrome P22 769
Maternal complications of pregnancy P01 761



Deaths due to neural tube defects include anencephalus, craniorachischisis, iniencephaly, spina bifida with and without hydrocephalus and encephalocele.

Maternal Mortality

Maternal Mortality

Maternal death is defined as one that occurs during pregnancy or within 42 days of the end of a pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by a woman's pregnancy, but not from accidental or incidental cause. Maternal mortality rates are calculated as the number of maternal deaths in a calendar year divided by the number of live births for the same period, multiplied by 100,000. The number of live births used in the denominator is an approximation of the population of pregnant women who are at risk of a maternal death. The numerator is calculated using data from the Final Mortality File from NCHS, included in these deaths assigned an underlying cause of death ICD-10 code of A34, O00-O95, or O98-O99. The denominator is calculated using data from the Natality File from NCHS.

Impact of Death Certificate Revision on Maternal Mortality Rates

The 2003 revision of the U.S. Standard Certificate of Death introduced a standard question format for maternal deaths and a separate pregnancy status item on the death certificate resulted in the identification of more maternal death. Therefore data beginning in 2003 may not be comparable to previous years.(1) To date the following states on the PeriStats web site have implemented the 2003 revision:

  • 2003: CA, ID, MT, NY
  • 2004: MI, NJ, OK, SD, WA, WY
  • 2005: CT, FL, KS, NE, NH, SC, UT
  • 2006: NM, OR, RI, TX, DC
  • 2007: DE, OH

This section of the web site will be updated as additional states implement the 2003 U.S. Standard Certificate of Death.

1. Hoyert DL, Heron MP, Murphy SL, Kung H. Deaths: Final Data for 2003. National vital statistics reports; vol 54 no 13. Hyattsville, MD: National Center for Health Statistics. 2006.

Medicaid Covered Births

Medicaid covered births, shown as a percentage of all births, is obtained from MCH Update, an annual publication published by the National Governors Association's (NGA). Data is collected by the National Governors Association Center for Best Practices, Health Policy Studies Division. Some states are unable to report the number of births paid for by Medicaid because some beneficiaries are enrolled in managed care programs that are unable to separate Medicaid and commercial enrollees. More background on NGA, as well as past issues of the MCH Update, can be found on the NGA Web site.

Medicaid Recipients and Expenditures

Medicaid recipients and expenditures statistics are obtained from the annual Medicaid Statistical Information System (MSIS) Report produced by the Centers for Medicare and Medicaid Services (CMS). States are required to submit all their eligibility and claims data to CMS on a quarterly basis through MSIS. Medicaid recipient data on PeriStats is for all non-disabled adults under the age of 65, excluding adults who are eligible because they are blind, and for non-disabled children, including children in foster care. PeriStats compares the percent of pregnant women, children and other non-disabled, non-elderly adults enrolled in Medicaid to the percent of total expenditures this population incurs. More background on the MSIS report can be found on the CMS Web site.

Newborn Screening

The National Newborn Screening and Genetics Resource Center (NNSGRC) provides the March of Dimes with newborn screening data on a continual basis. With funding from the federal Health Resources and Services Administration (HRSA), NNSGRC tracks the screening status in each state for each of the 31 core newborn screening conditions adopted by the Secretary of Health and Human Services in 2010. The 31 core newborn screening conditions include 29 conditions recommended in a 2004 report developed by the American College of Medical Genetics (ACMG) and 2 new conditions, severe combined immunodeficiency, and critical congenital heart defects recommended by the Secretary's Advisory Committee on Heritable Disorders in Newborns and Children (SACHDNC) in 2010. NNSGRC also tracks secondary target conditions that are not available on the PeriStats web site. Data is based on voluntary information provided by state newborn screening programs and reflects the most up-to-date information in the United States. NNSGRC publishes this information in the National Newborn Screening Status Report. Through the PeriStats web site, the March of Dimes Perinatal Data Center makes the data available in a series of 31 downloadable United States maps. While the data on the NNSGRC and PeriStats web sites is synchronized, it is possible that some state data may not be current due to lag time in state reporting.

Information from NNSGRC's National Newborn Screening Status Report is collapsed into three categories on the PeriStats condition-specific maps:


PeriStats Map Legend NNSGRC Status Report Symbol
Light Blue: Universally required by law or rule
Medium Blue: Testing required but not yet implemented C
Dark Blue: Not universally required by law or rule A,B,D, or not testing



A: universally offered but not yet required.
B: offered to select populations or by request.
D: likely to be detected and reported as a by-product of MRM screening targeted by law or rule.



Below each map is the estimated percent of live births screened for the core condition. This percentage is based on the sum of live births in states where newborn screening for the condition is universally required by law or rule divided by all live births in the United States and multiplied by 100.

Obesity

Obesity among women is derived from the Behavioral Risk Factor Surveillance Survey (BRFSS). The BRFSS is a health survey conducted by 50 states, 3 territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Obesity is part of a standard core of questions asked every year.

Methodological changes to the BRFSS in 2011 have affected the trends in prevalence estimates and they are not comparable to earlier years. The changes include the addition of cellular phones and improvements in the statistical weighting methods. More info can be found on the CDC Web site.

Calculations for BRFSS Obesity indicators are performed by the March of Dimes Perinatal Data Center, and include the percent of women of childbearing age (18-44 years) defined by BRFSS to be obesity. Body Mass Index (BMI) is a number calculated from a person's weight and height. Obesity is defined as persons who have a Body Mass Index of 30 or more. US rate is the median of states which reported that year. More background can be found on the BRFSS Web site.

Pregnancy Risk Assessment Monitoring System (PRAMS)

The Pregnancy Risk Assessment Monitoring System (PRAMS) from the Centers for Disease Control and Prevention (CDC) and state health departments, collects state-specific, population-based data to monitor maternal and child health indicators. Each state samples women who have recently had a live birth by drawing from the birth certificate file. Data are weighted in order to provide representative estimates of a state?s population. Because the data are based on a weighted sample, PeriStats also displays 95% confidence intervals, provided by the CDC, to assist with interpretation of rates and comparisons (see also FAQ on confidence intervals).

For more on PRAMS methods and questionnaires, visit the PRAMS website.

Select PRAMS data are available on PeriStats, including the following subtopics, with many also available stratified by maternal race/ethnicity, maternal age, household income, and Medicaid status:

  • Alcohol use, before pregnancy
  • Alcohol use, during pregnancy
  • Smoking, before pregnancy
  • Smoking, during pregnancy
  • Smoking, quit during pregnancy
  • Smoking, postpartum
  • Medicaid coverage, prenatal care
  • Medicaid coverage, before pregnancy
  • Medicaid coverage, anytime
  • Uninsured, before pregnancy
  • WIC status
  • Income
  • Vitamin use
  • NICU admission
  • Breastfeeding
  • Postpartum follow up
  • Sleep position

Population

Population data are shown for three major categories: total population, population of women 15-44 years of age, and total population of children less than 19 years. The data provided are from the following Census estimates; 1996 to 1999 are based on the 1990 Census, 2000 to 2009 are based on the 2000, and years 2010 and later are based on the 2010 Census. Distribution by race and race/ethnicity is also provided for total population, women 15-44 years and children less than 19 years, and by age for women 15-44 years. Beginning with the 2000 Census, race and ethnicity were reported according to standards published by the Office of Budget and Management, which were inconsistent with the reporting of race on vital records, including the birth certificate. In order to adjust for this, the Census Bureau released special population estimates that bridged the gap between these two sources of data. More information on this procedure and the data files can be found at the NCHS Web site.

Prenatal Care

Note: In 2003 states started to implement the 2003 revision of the U.S. Standard Certificate of Live Birth. This significantly impacts the ability to compare temporal and regional prenatal care data. See detailed description below.


Timing of Prenatal Care

Timing of prenatal care calculations stratify the timing of the mother's entry into prenatal care into three categories. These categories include: "Early prenatal care," which is care started in the 1st trimester (1-3 months); "Second trimester care" (4-6 months); and "Late/no prenatal care," which is care started in the 3rd trimester (7-9 months) or no care received. Calculations are based on the number of live births to mothers in a specific prenatal care category divided by all live births excluding those missing data on prenatal care, multiplied by 100.

Adequacy of Prenatal Care

Adequacy of prenatal care calculations are based on the Adequacy of Prenatal Care Utilization Index (APNCU), which measures the utilization of prenatal care on two dimensions. The first dimension, adequacy of initiation of prenatal care, measures the timing of initiation using the month prenatal care began reported on the birth certificate. The second dimension, adequacy of received services, is measured by taking the ratio of the actual number of visits reported on the birth certificate to the expected number of visits. The expected number of visits is based on the American College of Obstetrics and Gynecology prenatal care visitations standards for uncomplicated pregnancies (1), and is adjusted for the gestational age at initiation of care and for the gestational age at delivery. The two dimensions are combined into a single summary index, and grouped into four categories: Adequate Plus, Adequate, Intermediate, and Inadequate. On the PeriStats web site, the percent of infants whose mothers received Adequate and Adequate Plus prenatal care are combined into one category, Adequate/Adeq+ prenatal care. Definitions for these categories include:

  • Adequate Plus: Prenatal care begun by the 4th month of pregnancy and 110% or more of recommended visits received.
  • Adequate: Prenatal care begun by the 4th month of pregnancy and 80-109% of recommended visits received.
  • Intermediate: Prenatal care begun by the 4th month of pregnancy and 50-79% of recommended visits received.
  • Inadequate: Prenatal care begun after the 4th month of pregnancy or less than 50% of recommended visits received.
  • Adequate/Adeq+ used on the PeriStats web site can be defined as prenatal care begun by the 4th month of pregnancy and 80% or more of recommended visits received.


A more detailed description of APNCU can be found in (2).


Impact of Birth Certificate Revision

The transition from the 1989 revision of the U.S. Standard Certificate of Live Birth to the 2003 revision has multiple implications for tracking rates of prenatal care in the United States.(3) First, the timing of prenatal care item has changed. For data collected using the 1989 revision (all data prior to 2003), the item was recorded as the month of pregnancy that prenatal care began as reported by the mother. In 2003 the item was changed to request the date (day/month/year) of the first prenatal care visit, as recorded in the prenatal care or medical record. As a result of these modifications, rates of prenatal care timing and adequacy from the 2003 revision are not comparable to data collected using earlier birth certificate revisions.

The state implementation of the 2003 revision also impacts U.S. and state temporal trends. While some states began using the revised birth certificate in 2003, the schedule for implementation varies by state. Therefore, starting in 2003, total U.S. rates of timing and adequacy of prenatal care are not reported due to data incompatibilities between states. Comparison of prenatal care between states on different implementation schedules will not be possible. Furthermore, some states have implemented the 2003 revision mid-year, and in these cases data for that year are not shown. In 2006 California did not adopt the 2003 revision of prenatal care items. California fully implemented the 2003 revision in 2007. In 2007 not all births in Michigan are reported based on the 2003 revision, and data are not shown for that year. Finally, New York State implemented the 2003 revision in 2004 and New York City implemented in 2008. Rates of prenatal care for New York state exclude New York City from 2004 to 2007. Data for New York City can be found separately under city/county data.

On the PeriStats web site, graph bars displaying prenatal care data based on the 2003 revision are shown in red instead of the standard blue color. Tables indicate the change with an asterisk (*). At the U.S. level, separate timing of prenatal care rates for total revised states are provided below the graph for the most recent year available. In addition, the functionality that allows you to make comparisons between regions has been removed from the prenatal care section of the web site. To date the following states on the PeriStats web site have implemented the 2003 revision:

  • 2003: PA, WA
  • 2004: FL (mid-year), ID, KY, NH (mid-year), NY (excluding New York City), SC, TN
  • 2005: KS, NE, PR, TX, VT (mid-year)
  • 2006: CA (partially), DE, ND, OH, SD, WY
  • 2007: CO, GA (mid-year), IA, IN, MI (partially)
  • 2008: MT, NM, New York City, OR
  • 2009: DC (mid-year), NV (mid-year), OK (mid-year), PR, UT
  • 2010: IL, LA (mid-year), MD, MO, NC (mid-year)
  • 2011: MA (mid-year), MN (mid-year), WI

Beginning with the 2011 data year, the National Center for Health Statistics no longer includes unrevised data for prenatal care on the data file.

This section of the web site will be updated as additional states implement the 2003 U.S. Standard Certificate of Live Birth.

  1. Standards for Obstetric-Gynecologic Services. 6th ed. Washington, DC: American College of Obstetricians and Gynecologists; 1985.
  2. Kotelchuck M. An evaluation of the Kessner Adequacy of Prenatal Care Index and a proposed Adequacy of Prenatal Care Utilization Index. Am J Public Health 1994; 84: 1414-1420.
  3. Martin JA, Hamilton BE, Sutton PD, et al. Births: Final data for 2003. National vital statistics reports; vol 54 no 2. Hyattsville, MD: National Center for Health Statistics. 2005.

Preterm Birth

Preterm birth rates are stratified into three categories on the PeriStats web site: very preterm (live birth prior to 32 completed weeks); late preterm (live birth delivered between 34 and 36 weeks); and preterm (live birth prior to 37 completed weeks, including both late and very preterm births). Live births at or beyond the 37th week of pregnancy, include term (37-42 weeks) and post-term (42+ weeks) births. Calculations are based on the number of live births to infants in a specific gestational age category divided by all live births excluding those missing data on gestational age, multiplied by 100. Singleton-specific rates are calculated the same way.

The March of Dimes Perinatal Data Center stratifies data by the gestational age categories listed above, however, the individual level algorithm for calculating gestational age in weeks was developed by the National Center for Health Statistics (NCHS). All individual level gestational age calculations are completed by NCHS prior to receiving electronic data. The following provides a detailed description of the NCHS algorithm, and uses data from 2001 as an example:

The primary measure used by NCHS to determine the weeks of completed gestation of the newborn is the interval between the first day of the mother's last normal menstrual period (LMP) and the infant's date of birth. In 2001, the gestational age for 95.1% of live births was calculated using LMP. LMP is reported as the day, month and year.

In cases where the day of LMP is missing (but the month and year are complete), NCHS assigns that record the weeks of gestation of the previous completed record in the file with a similar race and birthweight and the same computed months of gestation. For these records, the gestational age is said to be 'imputed'. The number of months of gestation needed for this process is computed for both missing-day records and completely reported records by subtracting the reported month of LMP from the reported month of birth.

In cases where the month, year, or entire LMP is missing, or when the calculated or assigned (imputed) gestational age appears to be inconsistent with birthweight, the clinical estimate of gestation is used (4.9% of live births in 2001).

In cases where the reported birthweight is inconsistent with both the LMP-computed gestational age and the clinical estimate, the LMP-computed gestational age is used and birthweight is reclassified as "not stated" (less than 0.01% of live births in 2001).

In cases where both the LMP and the clinical estimate are missing, gestational age is set to 'missing.' In 2001, 0.1% of live births were missing gestational age.

As with other indicators, preterm birth rates on PeriStats may differ from those provided directly by state health departments. This may be due to differences in the way the health department and NCHS calculate the gestational age of the infant or in the handling of missing data.

Additional detail on the NCHS algorithm for calculating gestational age can be found in:

  • National Center for Health Statistics, S. Taffel, D. Johnson, and R. Heuser: A method of imputing length of gestation on birth certificates. Vital and Health Statistics. Series 2, No. 93. DHHS. Pub. No. (PHS) 82-1367. Public Health Service. Washington. U.S. Government Printing Office, May 1982.
  • Martin JA, Hamilton BE, Ventura SJ, Menacker F, Park MM, Sutton PD. Births: Final data for 2001. National vital statistics reports; vol 51 no. 2. Hyattsville, Maryland: National Center for Health Statistics. 2002.

PubMed Searches

PubMed search strategies on the PeriStats Web site were developed by the New York Academy of Medicine (NYAM), in collaboration with the March of Dimes Perinatal Data Center (PDC). PubMed provides Web access to bibliographic information, and was created by the National Library of Medicine (NLM). Through PeriStats, users can obtain the most current maternal and infant health literature within a one-year timeframe, or can opt to search PubMed without a temporal filter.

PubMed search results were reviewed by the PDC between December 2004 and March 2005. Articles are continuously added to the PubMed database, thus search results will vary over time. It takes approximately 6-8 weeks after publication for articles to be added to the database, so results often exclude articles published during this initial time period. Searches were designed to be highly selective and retrieve the most relevant articles. Such specificity may exclude articles of interest to the user. Results are meant to be a starting point for obtaining the latest maternal and infant health literature, and may require refinement for each user's needs. Search strategies can be modified within PubMed. If you require assistance refining your search in PubMed, please contact a medical librarian. For a fee, NYAM provides research and document delivery services - please call (212) 822-7300 for details.

Sexually Transmitted Disease

Sexually transmitted disease (STD) statistics on PeriStats were obtained from Division of STD Prevention (DSTD), National Center for HIV, STD, and TB Prevention (NCHSTP), Centers for Disease Control and Prevention (CDC). They acquire this data from STD control programs and health departments in the 50 States, the District of Columbia, selected cities, counties, U.S. dependencies and possessions, and independent nations in free association with the United States. Rates for chlamydia, gonorrhea, and syphilis are reported as rates per 100,000 women. Congenital syphilis is reported as a rate per 100,000 live births. Rates for syphilis and congenital syphilis are 5-year averages. More background can be found at the DSTD Web site.

Singleton and Multiple Birth Rates

Singleton and multiple birth rates are shown for all births, by maternal race, maternal race/ethnicity and maternal age. Multiple birth deliveries are further stratified by twin deliveries and triplet and higher order deliveries. The singleton delivery rate is calculated as the number of singleton live births divided by all live births, multiplied by 100. All multiple birth calculations are shown as a ratio rather than a percent, and are multiplied by 1000 instead of by 100, consistent with NCHS procedures. This is a ratio, as opposed to a rate, because sets of multiples cannot be determined from the data. Therefore, counts in the numerator represent individual live births that occur from multiple deliveries. Low birthweight, very low birthweight, preterm and very preterm birth rates among singletons and multiples are also shown (see calculation notes on Birthweight and Preterm birth for more information).

Smoking

Smoking among women and men is derived from the Behavioral Risk Factor Surveillance Survey (BRFSS). The BRFSS is a health survey conducted by 50 states, 3 territories, and the District of Columbia, and is the primary source of information on health-related behaviors of Americans. Questions are related to chronic diseases, injuries, and infectious diseases that can be prevented. States use standard procedures to collect data through a series of monthly telephone interviews with adults. The BRFSS questionnaire is developed jointly by Centers for Disease Control and Prevention and state health departments and includes five sections. Cigarette use is part of a standard core of questions asked every year.

Methodological changes to the BRFSS in 2011 have affected the trends in prevalence estimates and they are not comparable to earlier years. The changes include the addition of cellular phones and improvements in the statistical weighting methods. More info can be found on the CDC Web site.

Calculations for BRFSS smoking indicators are performed by the March of Dimes Perinatal Data Center, and include the percent of women of childbearing age (18-44 years) and of men 18 years and older defined by BRFSS to be smokers. Smokers are defined as persons who have ever smoked 100 cigarettes and currently smoke every day or some days. U.S. rate is the median of states which reported that year. More background can be found on the BRFSS Web site.

Title V

Title V Funding figures are obtained from the Maternal and Child Health Bureau (MCHB), a department of the Health Resources and Services Administration, U.S. Department of Health and Human Services. Title V of the Social Security Act has authorized the Maternal and Child Health Services Program since 1935 and is a major source of state funds for women of childbearing age, infants and children with special health care needs. Title V consists of block grants to state health agencies on the basis of specified formulas, and discretionary grants referred to as Special Projects of Regional and National Significance. States must provide a three-dollar match for every four federal dollars allocated. PeriStats makes available the amount of federal dollars allocated to each state as well as the amount matched by each state and Washington, DC. US totals shown in PeriStats include funding to all 50 states and the District of Columbia, but exclude funding to territories. More background is available on the MCHB Web site.

Uninsured Women and Children

The percent of uninsured women (15-44 years of age) and children (<19 years) is obtained from the U.S. Census Bureau. Estimates of uninsured women and children by state are reported as a three-year average in order to ensure reliability of rates. Children <19 include all individuals under the age of 19, regardless of whether they are dependents. Data is collected by the Census using the Current Population Survey (CPS), a monthly survey of about 50,000 households. The sample is selected to represent the civilian non-institutional population. More background can be found at the CPS Web site.

Women, Infants and Children (WIC) Program

The Special Supplemental Nutrition Program for Women, Infants and Children (WIC), is a federally funded program administered by the U.S. Department of Agriculture (USDA), state health departments, city and county health departments and community health clinics. The program serves low-income women, infants and children who are low income and nutritionally at risk. At the beginning of each fiscal year (October 1) a state receives a WIC allocation for food and an allocation for nutrition services and administration. A state may receive additional funds mid-year. PeriStats makes available the number of women and children served by WIC for each state and Washington, DC. Data shown in PeriStats includes participants served by state health departments and excludes those receiving services from the Inter-Tribal Organizations. More background on WIC can be found at the USDA Web site.