Live births to mothers with low Body Mass Index (3-year average)

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Definitions: Percent of live births to mothers with a low Body Mass Index (BMI). Mothers’ low BMI presented here are calculated by dividing the number of live birth babies whose mothers had low BMI at the time of birth in three consecutive calendar years by the total number of live births reported in the same period.

Data Source: The data used for this measure come from Center for Health Statistics, Washington State Department of Health (DOH), Birth Data. Data were retrieved on May 18, 2016 at http://www.doh.wa.gov/DataandStatisticalReports/VitalStatisticsData/BirthData/BirthTablesbyTopic.aspx (Natality Table B6).

The DOH combines information from the Washington State Birth and Death Certificate Systems to produce records of all infant deaths occurring in the state and nearly all infant deaths to residents of the state. Information about the birth is collected in hospitals and birth centers. Information about the death is collected by funeral directors from an informant (usually a family member).

S: Data estimate has been suppressed. Percents are not shown when the average number of live birth babies whose mothers had low BMI over the three consecutive years is fewer than 10.

Footnotes: Data last updated in May 2016 by Washington KIDS COUNT.

BMI is calculated using the weight and the height of an individual in the following formula: BMI = (703.1 x weight in lbs)/square of height in inches. The Center for Disease Control and Prevention (CDC) classifies BMI into four categories. When the values are less than 18.5, BMI is considered low. Low BMI is also referred to as being underweight.

According to DOH technical notes available online at http://www.doh.wa.gov/Portals/1/Documents/5300/TechnicalNotes.pdf, “these events are rare in annual terms. When the events are rare (small numbers) data may be affected by random fluctuations in the number of events between successive years. The effect of such random fluctuations on death rates is proportionately larger when the number of events is small. For example, one more fetal death has a larger numerical impact on an area with 3 deaths than it does on an area with 300 deaths. Because of these random fluctuations, the rates based on small numbers may not be as reliable as those based on larger numbers in the sense that they may have limited predictive value.”

We combined three years of data to minimize unreliability of measurement due to small numbers. The values reported here refer to rolling averages across three years. For instance, we report the average value across the years 2003, 2004 and 2005.