About the birth outcomes data

This page provides general information about the birth outcomes data and measures developed by the Minnesota Environmental Public Health Tracking Program. For more information about these data, contact Minnesota Public Health Data Access.

 

  • The numbers and rates of prematurity, low birth weight, infant mortality, and sex ratio in Minnesota by year and race/ethnicity.
  • If certain birth outcomes are going up or down over time.
  • If a segment of a population is at increased risk for adverse birth outcomes.
  • To inform the public about adverse birth outcomes.
  • For program planning and evaluation by state and local partners.
  • The causes of birth outcomes
  • Environmental exposure-related causes of adverse birth outcomes are only one piece of a puzzle that includes many other factors such as access to and quality of health care, maternal characteristics, genetic factors, behavioral factors, childcare skills, and injury prevention. Many of these factors are not included in birth or death records. Variables that are included are often difficult to interpret without additional information on social and behavioral factors.

Birth and death certificates and fetal death reports filed with the MDH Office of the Vital Records are the data sources for the birth outcomes measures. These data are entered electronically into the Minnesota Registration and Certification (MR&C) system, an integrated, web-based application that electronically records and maintains records on vital events (birth, death, and fetal death) for the State of Minnesota. At the end of each calendar year, the Minnesota Center for Health Statistics prepares statistical files for analysis. 

Measures are computed using data on births to Minnesota resident mothers, with residency determined by address at time of birth as listed on the birth certificate. Race and ethnicity categories for births are based on the race and ethnicity of the mother as reported on the birth certificate. Hispanic ethnicity includes anyone indicating they are of Hispanic/Latino descent regardless of race.

The National Center for Health Statistics is the source for national numbers on these pages (via CDC WONDER).

  • Birth outcomes are identified from birth and death certificates and fetal death reports filed with the MDH Office of the Registrar. Fields used from birth certificates include gestational age, birth weight, sex of infant, race of mother, and age of mother. Age at death is obtained from death certificates linked to birth certificates. Fetal deaths are identified from death certificates. Fields used from death certificates include gestational age, race of mother, and age of mother.
  • Prematurity: A premature or preterm birth is birth less than 37 weeks gestation. Beginning in 2012, gestation is based on the obstetric estimate of gestational age. Prior to that, gestation was determined by the last menstrual period (or by imputing gestational age when date of last menstrual period was missing from the birth certificate). Since gestation using last menstrual period and obstetric estimate can be quite different, they should not be compared. According to the National Center for Health Statistics, there are fewer premature births when using the new method (obstetric estimate). Measures are calculated by using a denominator that includes cases with missing information for that measure. 
  • Low Birth Weight: A low birth weight baby is a baby born weighing less than 2,500 grams (5 pounds, 8 ounces). Measures are calculated by using a denominator that includes cases with missing information for that measure. Low birth weight as shown here uses only full-term (37+ weeks gestation), singleton births. Very low birth weight as shown here uses only singletons, regardless of gestational age.
  • Infant Mortality: Mortality data are calculated using the period linked approach, where all infant deaths occurring in a given data year are linked to their corresponding birth certificates, whether the birth occurred in that year or the previous year. For example, the 2010 mortality data includes all infant deaths occurring in 2010 that have been linked to their corresponding birth certificates, whether the birth occurred in 2009 or in 2010. An alternative method sometimes used is the birth cohort linked file approach, which consists of deaths to infants born in a given year. In both cases, the denominator is all births occurring in the year. 

Race and ethnicity is self-selected on the birth certificate and corresponds with the mother’s race and ethnicity. The categories presented here represent maternal race according to the NCHS bridged race algorithm. There is an option to self-select "other" and if there is missing information the maternal race is designated as "unknown."

In 2016, about 3,200 mothers self-reported other or unknown race. The majority of these mothers were categorized as Hispanic based on their responses in the “other” field (e.g., Salvadoran or Peruvian). About 2,000 mothers remain in the “other” race category after the bridged race algorithm was applied and about 350 births were classified as “unknown” race. In 2016, that means mothers are “other” race for about 3 percent of the birth cohort and “unknown” rate for less than 1 percent of the birth cohort.

Number:

  • The number indicates the total number of a birth outcome.
  • If you want to understand the magnitude or how large the overall burden is, use the number.

Rate:

  • A rate is a ratio between two measures with different units. In our analysis a rate is calculated using a numerator (the number of a birth outcome during a period of time) divided by a denominator (the number of people at risk in a population during the same period of time, the number of live births). This fraction is then multiplied by a constant to make the number easier to understand. The constant is 100 for premature, very premature, low birth weight, and very low birth weight (also called percent), or 1,000 for infant mortality measures.
  • If you want to understand the probability or the underlying risk in a population, then use a rate.
  • Rates based on counts less than 20 are unstable and are not shown. These rates are unstable because they can change dramatically with the addition or subtraction of one case.
  • The quality of vital statistics data is directly related to the completeness and accuracy of the information contained in the source documents. MDH maintains two programs to improve the quality of information received on birth and death certificates in order to ensure that the information is as complete and accurate as possible: a query program to contact hospital personnel, funeral directors, and/or physicians concerning incomplete or conflicting information; and a field program focused on educating participants in the vital registration system. MDH also holds birth registration annual conferences to improve birth and death data entry.
  • Estimates of the length of a pregnancy ("gestational age") were included in most Minnesota birth certificate records. Whether a birth record has this information will affect measures of premature, very premature, and full-term low birth weight. 
    • About 11 percent of all singleton birth records between 2000 and 2011 were missing gestational age each year.
    • About 13 percent of all singleton birth records between 2012 and 2016 were missing gestational age each year. This has improved over time, with only 9 percent missing gestational age by 2016.
  • Timeliness is a limitation of the vital records system. It is not unusual for a birth record to be amended weeks or months after it was originally processed by the Center for Health Statistics due to adoption, correction, or out-of-state birth. Because of the time it takes to correct and amend birth records, the final birth file for a particular calendar year can take many months after the end of the calendar year to close and be made available for epidemiological use. Data on infant deaths takes even longer to be ready for analysis because of the time it takes to link birth and death files.
  • Residential information is very important when examining environmental exposures and other risk factors that may occur before birth. A limitation of the data source is that the place of residence during pregnancy (and, with infant death, residence during first year of life) may not be represented by maternal residence at time of birth (or death). Adoption replaces demographic characteristics of the birth mother (including mother's race/ethnicity, education level, etc.) with those of the adoptive mother. Replacement of birth mother address with adoptive mother address further biases the place of residence data element.

For more about the birth outcome data and measures developed by the MN Environmental Public Health Tracking Program, contact Minnesota Public Health Data Access. To learn more about additional birth outcomes data available from MDH, contact the MN Center for Health Statistics