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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.

Birth Order

The total number of live births to this mother, up to and including this birth.

Birthweight

The newborn’s weight is reported in grams, or pounds and ounces (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 an age group.

Gestational Age, Prematurity

Gestational age is based on the computed difference between the date of last normal menses and the date of the infant’s birth. If the date of last normal menses is missing or the computed difference is less than 16 weeks or more than 45 weeks, then the clinical estimate of gestational age reported by the attending physician is substituted. This minimizes the number of births with unknown gestational age.

  • 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 32 to 36 weeks are "moderately 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).

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.

Interval Since Last Delivery

The time between the mother’s last live birth and this delivery. This measure is computed from the birth date and the reported month and year of last live birth. Unlike the Inter-Pregnancy Interval, it includes the gestation period of the current birth. Multiple births have the same interval. Intervals of less than seven months or more than 30 years were coded as ‘missing.’

Inter-Pregnancy Interval

The time between the end of the mother’s last pregnancy and the estimated date of conception for this pregnancy. The reported month and year of the mother’s last live birth is the best available measure of the end of the last pregnancy. The beginning of this pregnancy is computed from the gestational age of this birth and the birth date.

Maternal Tobacco Use

Based on mother’s report of smoking during pregnancy (Yes/No indicator). Does not measure amount or duration of tobacco use during pregnancy.

City of Milwaukee ZIP Codes

Birth Modules: ZIP code of mother’s mailing address, for those mothers reporting their residence is in the City of Milwaukee. WISH birth data modules offer the 24 individual ZIP codes with 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.

Note: In previous editions of WISH, the following eight ZIP codes were grouped into one category: 53204, 53205, 53206, 53208, 53212, 53215, 53216, and 53233. All other ZIP codes reported by City of Milwaukee residents were grouped into a second ‘other’ category.

Mother’s Race and Ethnicity

Six groups based on first reported race of mother, and whether or not mother reported Hispanic/Latina ethnicity. The groups are:

  • White (Non-Hispanic)
  • Black (Non-Hispanic)
  • American Indian (Non-Hispanic)
  • Hispanic
  • Laotian / Hmong (Non-Hispanic)
  • Other (Non-Hispanic, almost entirely Asian)

Newborn Transferred to Another Hospital

Whether the infant was transferred from the birth hospital to a different hospital.

The birth hospital reports whether the infant was ‘treated in an NICU or transferred to another hospital’ and also reports the name of the transfer/NICU hospital, which may be itself. If this item is checked on the birth report and the transfer/NICU hospital is not the birth hospital, then this is coded ‘yes.’

NICU Utilization

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 reports whether the infant was ‘treated in an NICU or transferred to another hospital’ and also reports the name of the transfer/NICU hospital, which may be itself. If this item is checked on the birth report and the birth hospital has a Level 3 NICU, then NICU Utilization is ‘yes.’ If this item is checked and the birth hospital reports transferring the infant to another hospital and that hospital has a Level 3 NICU, then NICU Utilization is also coded as ‘yes.’

Number of Previous Pregnancies

The number of previous pregnancies for this mother, regardless of outcome (live birth, miscarriage, other outcome).

Single or Multiple Birth

Plurality: the number of fetuses in this pregnancy (single, twins, triplets, etc.). Not all may result in live births.

Prenatal Care, Adequacy of Prenatal Care

Two 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.

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.

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.

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Last Revised:  July 18, 2010