WISH: Definitions of Measures Used in Birth-Related Modules
The information in the WISH birth-related modules is from Wisconsin resident birth certificate data. The Infant Mortality module is based on both birth data and death certificate data.
On January 1, 2011, the Wisconsin State Vital Records Office began collecting birth certificate information based on the 2003 U.S. Standard Certificate of Live Birth using a new electronic system. Before January 1, 2011, Wisconsin had been collecting birth certificate information based on the 1989 U.S. Standard Certificate of Live Birth. Birth data collection changed in many ways when Wisconsin began using the 2003 U.S. Standard Certificate of Live Birth. For a detailed description of changes, please see Technical Notes: Wisconsin Births and Infant Deaths, 2011 (P-45364-11) and Births to Teens in Wisconsin, 2011 (P-45365-11) (PDF).
Beginning in 2011, height and pre-pregnancy weight of the mother were collected on the birth record. A mother's body mass index (BMI) was calculated based on these measures.
The total number of live births to this mother, up to and including this birth.
The newborn's weight is reported in grams, or in pounds and ounces and converted to grams.
- Low birthweight: Infants weighing less than 2,500 grams (about 5.5 pounds) at birth.
- Very low birthweight: Infants weighing less than 1,500 grams (about 3.3 pounds) at birth.
- Extremely low birthweight: Infants weighing less than 1,000 grams (about 2.2 pounds) at birth.
Fertility Measures
- Birth Rate or Crude Birth Rate: The number of live births per 1,000 total population.
- General Fertility Rate: The number of live births per 1,000 females ages 15-44.
- Age-specific Fertility Rate: The number of live births per 1,000 females in a specific age group.
Prior to the 2014 data year update, WISH used an estimate of gestational age based on the computed difference between the date of reported last normal menses and the date of the infant's birth. Beginning with the 2014 data year update, WISH uses an estimate of gestational age that is based on the attending physician's clinical estimate of gestational age. The CDC's National Center for Health Statistics is transitioning to the obstetric estimate as documented in National Vital Statistics Reports, Volume 64 Number 5, June 1, 2015 (PDF). WISH now uses an estimate of gestational age that is calculated in a comparable manner. The CDC's evaluation indicates that compared to the estimate based on the time since the mother's last menstrual period, the obstetric estimate results in a smaller proportion of premature births.
- Premature or preterm: Births are classified as premature (less than full term) if the gestational age was less than 37 weeks. Births before 32 weeks of gestational age are "very preterm." Those at 32 to 35 weeks are "moderately preterm" and those at 36 weeks are "late preterm."
- Premature low birthweight: Births that have both a gestational age of less than 37 weeks and a birthweight of less than 2,500 grams (about 5.5 pounds).
- Term low birthweight: Full-term births with low birthweight; that is, births that have a gestational age of 37 weeks or more and a weight at birth of less than 2,500 grams (about 5.5 pounds).
Beginning in 2011, information on vaccines and immune globulins administered to newborns in the hospital was collected on the birth record. Note that the birth record includes only vaccines and hepatitis B immune globulin administered shortly after birth. (Immunization data for all infants/children is available from the Wisconsin Immunization Registry.)
Beginning in 2011, the birth record collected information on whether or not the infant was breastfed before being discharged from the hospital.
Infant Mortality
Infant mortality refers to deaths that occur within the first year of life.
- Infant mortality rate: The number of infant deaths per 1,000 live births during the year.
- Neonatal mortality: Infant deaths that occur before 28 days of age.
- Postneonatal mortality: Infant deaths that occur from 28 to 364 days of age.
The time between the mother's last live birth and this delivery. This measure is computed from the infant's date of birth and the reported month and year of the previous last live birth. Unlike the Inter-Pregnancy Interval, it includes the gestation period of the current birth.
The time between the end of the mother's last pregnancy resulting in a live birth and the estimated date of conception for this pregnancy. The beginning of this pregnancy is computed from the gestational age of this birth and the birth date.
Beginning in 2011, additional categories for describing the method of delivery were added: vaginal/spontaneous, vaginal/forceps, vaginal/vacuum, cesarean, and unknown. Additional fields collected under the Risk Factors checklist ask if the mother had any previous cesarean deliveries and, if so, how many. Information from the previous cesarean deliveries field was combined with information from the field for final route and method of delivery to define vaginal birth after cesarean (VBAC), primary C-section, and repeat C-section deliveries. However, there are birth records for which the previous cesarean deliveries item was not completed (unknown) and cesarean was indicated as the final route and method of delivery. Those records were categorized as C-section (unknown if primary or repeat).
Three groups based on mothers country of birth: United States, Foreign Born, Unknown/Not Classifiable.
Beginning in 2011, information on mother's education was collected in different categories than for previous years. This resulted in two education measures:
- Education (7 categories): Mother's education in categories consistent with how mother's education was collected prior to 2011.
- Education (9 categories): Mother's education as collected beginning in 2011. The old categories could not be configured into these new categories, so only birth records beginning in 2011 are included. The new categories modify the measures of post-high school education.
Seven groups based on reported race of mother and whether or not the mother reported Hispanic/Latina ethnicity. The groups are:
- White (Non-Hispanic)
- Black/African American (Non-Hispanic)
- American Indian/Alaska Native (Non-Hispanic)
- Hispanic
- Laotian or Hmong (Non-Hispanic)
- Other (Non-Hispanic)
- Two or more races (Non-Hispanic)
The category titled "Two or more races (Non-Hispanic)" is only available from 2011 forward.
Indicates whether the mother reported receiving food from the WIC program for herself during pregnancy.
Beginning in 2011, this indicates whether the newborn was transferred from the birth hospital to a different hospital within the first 24 hours.
Prior to 2011, the definition was whether the infant was transferred from the birth hospital to a different hospital. The birth hospital reported whether the infant was 'treated in an NICU or transferred to another hospital' and also reported the name of the transfer/NICU hospital, which may have been the birth hospital itself. If this item was checked on the birth report and the transfer/NICU hospital was not the birth hospital, then this was coded 'yes.'
Indicates whether the infant was admitted to a neonatal intensive care unit, either in the birth hospital or in a hospital to which the infant was transferred from the birth hospital.
Prior to 2011, the definition was whether the infant was treated in a Level 3 neonatal intensive care unit, either in the birth hospital or in a hospital to which the infant was transferred from the birth hospital. The birth hospital reported whether the infant was 'treated in an NICU or transferred to another hospital' and also reported the name of the transfer/NICU hospital, which may have been the birth hospital itself. If this item was checked on the birth report and the birth hospital had a Level 3 NICU, then NICU Utilization was 'yes.' If this item was checked and the birth hospital reported transferring the infant to another hospital and that hospital had a Level 3 NICU, then NICU Utilization was also coded as 'yes.'
The number of previous pregnancies for this mother, regardless of outcome (live birth, miscarriage, other outcome).
Plurality: the number of fetuses in this pregnancy (single, twins, triplets, etc.). Not all may result in live births.
Trimester prenatal care began: Prior to 2011, the month prenatal care began was reported by the birth hospital and grouped by trimester. Beginning in 2011, the month prenatal care began is calculated from the date of last normal menses and the date of first prenatal care visit.
Due to changes in the standard birth certificate, the measure for percent of births to mothers who received first trimester prenatal care is not comparable to the measure used in previous years, starting in 2008 for U.S. data and in 2011 for Wisconsin data.
Two other common measures of adequate prenatal care are the 'Kessner Index' and the 'Kotelchuck Index,' both of which consider the month care began and the number of visits, taking into account the gestational age at delivery (preterm births mean less time for prenatal care visits).
The Kessner Index of Prenatal Care Adequacy uses the following classifications for a full-term birth:
- Adequate: Initiation in the first trimester with nine or more visits.
- Intermediate: Initiation in the first trimester with five to eight visits, or initiation in the second trimester with five or more visits.
- Inadequate: Initiation in the second trimester with one to four visits, or initiation in the third trimester with one or more visits.
- None: No prenatal care.
The number of visits is adjusted for preterm births.
The Kotelchuck Adequacy of Prenatal Care Utilization Index also takes into account the month that prenatal care began and the number of prenatal visits, and adjusts for gestational age. It includes categories for adequate, intermediate, and inadequate levels of prenatal care utilization. The number of prenatal visits is compared to the expected number for gestational age, based on the American College of Obstetricians and Gynecologists prenatal care standards for uncomplicated pregnancies.
Beginning in 2011, the principal source of payment for the delivery was collected. Please use caution when using this field. The information reported by the hospital on the birth record may change weeks to months after the birth, due to coordination of benefits and Medicaid eligibility changes. This field is not the definitive source of information about payment for this delivery.
Teen Births
Births to women less than 20 years of age are considered teen births. This group is often divided into older teens (18-19) and younger teens (15-17). Very few births occur to females under age 15 and they are included in counts and rates for the 'under 18' and 'under 20' groups.
- Teen birth rate: The number of births to mothers less than 20 years of age per 1,000 females ages 15-19.
- Tobacco use during pregnancy: Indicates whether the mother smoked during the pregnancy. Mothers who smoked in the three months prior to pregnancy but did not report smoking during the pregnancy are excluded from this measure. Does not measure the amount or duration of tobacco use during pregnancy.
- Maternal smoking: Beginning in 2011, the mothers smoking status before and during pregnancy in six categories was collected. Does not measure the amount or frequency of tobacco use during pregnancy. This field is calculated in the following ways:
- Did not smoke - Mothers who reported they did not smoke at any point before or during pregnancy.
- Quit prior to pregnancy - Mothers who reported smoking in the three months prior to pregnancy but not smoking at all during pregnancy.
- Quit first trimester - Mothers who reported smoking in the three months prior to pregnancy and the first trimester but who did not smoke during the remainder of the pregnancy.
- Quit second trimester - Mothers who reported smoking in the three months prior to pregnancy, in the first trimester, and in the second trimester, but who did not smoke in the third trimester. Only births with a gestational age greater than 28 weeks are included in this category.
- Smoked entire pregnancy - Mothers who reported smoking in the three months prior to pregnancy, in the first trimester, in the second trimester and/or in the third trimester. This category includes preterm births to mothers who smoked through the second trimester and full-term births to mothers who smoked through the third trimester.
- Smoked intermittently throughout pregnancy - Mothers who reported smoking on and off throughout the pregnancy.
Beginning in 2011, licensed midwives were added as a distinct category. In Wisconsin, these midwives are licensed through the Department of Safety and Professional Services.
Birth Modules: ZIP code of mothers mailing address, for those mothers reporting their residence is in the City of Milwaukee. WISH birth data modules offer the 24 individual ZIP codes that have had at least 1,000 births since 1989. All other Milwaukee ZIP codes are grouped into an 'other' category.
Infant Mortality Module: ZIP code of infant's residence at time of death, for those infants whose residence was in the City of Milwaukee. This module offers the same ZIP code choices as in the birth modules.