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The Maternal Infant Health Assessment (MIHA) survey is an annual statewide representative survey of individuals with a recent live birth in California. MIHA collects self-reported information about maternal and infant experiences before, during, and shortly after pregnancy. Read More

MIHA is led by the Maternal, Child and Adolescent Health Division in the California Department of Public Health (CDPH) in collaboration with: CDPH Women, Infants and Children (WIC) Division and the Center for Health Equity at the University of California, San Francisco (UCSF).

Included below:

• Data Analysis
  
• Subgroup Definitions
  
• Indicator Definitions
  
• MIHA County-Level Data Availability
  
• MIHA Regions of California
  
• Data Annotation and Suppression Criteria
  
• Weighting Methods used in publications of MIHA data
  
  

Data Analysis

The percentage and estimated number of pregnant or birthing people in the population with a given health indicator or characteristic are best estimates of the actual prevalence in the population. The 95% confidence interval (95% CI), comprised of the lower 95% confidence limit (Lower 95% CL) and upper 95% confidence limit (Upper 95% CL), indicates that there is a 95% chance that the range contains the actual prevalence in the population. The state, county, and regional data included in the dashboards use three-year aggregated data for the percent and 95% CI, and the annual estimate shown is a three-year average.

Annotation and Suppression

The relative standard error (RSE) is used to measure the statistical reliability of survey estimates. Estimates that should be interpreted with caution due to low statistical reliability (RSE between 30% and 50%) are noted with an asterisk (*) in the MIHA Data Snapshots or in tooltips in the MCAH Data Dashboards, and with a “1” or “Yes” in the Annotated column of the downloadable data table. 

The percent, 95% CI, and annual population estimate are suppressed when the RSE is greater than 50% or could not be calculated, sample numerator is less than five, or the weight population denominator is less than 100. Suppression is noted with a double dash (--). 

For more details see Data Annotation and Suppression Criteria and Weighting Methods.

Subgroup Definitions

Subgroups are based on self-reported data from the MIHA survey or the birth file, and refer to the most recent birth, or pregnancy for the most recent birth, unless otherwise indicated. Any change to a subgroup or subgroup category is noted in the Change in Definition and/or Comparability column(s). Subgroups and subgroup categories listed here are those that have been used in MIHA data publications since 2010.

Indicator Definitions

Indicators are based on self-reported data from the MIHA survey and refer to the most recent birth, or pregnancy for the most recent birth, unless otherwise indicated. Unless noted, the denominator for each indicator includes all individuals with a live birth. Any change to a survey question or indicator, compared to how it was in a prior year, is noted in the Change in Definition and/or Comparability column(s). Indicators listed here are those that have been used in MIHA data publications since 2010.

• Prior Poor Birth Outcomes

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  Prior Poor Birth Outcomes

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Prior low birth weight or preterm delivery	Prior to the most recent birth, ever had a baby weighing <2,500 grams at birth or born at <37 weeks gestation.	2010-2012	None ---	None ---
  Prior delivery by c-section	Ever had a cesarean section prior to the most recent birth, reported on the birth certificate.	2010-2012	None ---	None ---

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• Health Status Before Pregnancy

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  Health Status Before Pregnancy

  Indicator	Definition	Years Available	Change in Definition	Comparability
  In good to excellent health	Self-rated health before pregnancy	2011-2021 for current definition;  2010 for previous definition.	Prior to 2011, definition included self-rated physical health. In 2011, the survey question was changed from two separate questions on physical health and mental health to one question on “health." Additional response of “Very good" was added between response categories “Excellent" and “Good."	Starting in 2011, the indicator is not comparable with prior years.
  Diabetes	Before pregnancy, told by a health care worker that they had diabetes (high blood sugar).	2013-2021 for current definition; 2010-2012 for previous definition.	Prior to 2013, definition also included diagnosis during this pregnancy with diabetes or with gestational diabetes.	Starting in 2013, the indicator is not comparable with prior years.
  Hypertension	Before pregnancy, told by a health care worker that they  had hypertension (high blood pressure).	2013-2021 for current definition; 2010-2012 for previous definition.	Prior to 2013, definition also included diagnosis during this pregnancy with hypertension, preeclampsia, eclampsia or toxemia.	Starting in 2013, the indicator is not comparable with prior years.
  Asthma	Before pregnancy, told by a health care worker that they had asthma.	2013-2021 for current definition; 2010-2012 for previous definition.	Prior to 2013, definition also included diagnosis of asthma during this pregnancy.	Starting in 2013, the indicator is not comparable with prior years.

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• Nutrition and Weight

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  Nutrition and Weight

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Daily folic acid use, month before pregnancy	During the month before pregnancy, took a multivitamin, prenatal vitamin or folic acid vitamin every day of the week.	2010-2018	None ---	None ---
  Overweight before pregnancy	Body Mass Index (BMI) was calculated from weight and height reported on the birth certificate. BMI of 25-29.9 is classified as overweight. BMI was calculated only for birthing people reporting height within 48-83 inches and weight within 75-399 pounds. BMI values outside of 13-69.99 are excluded. BMI may overestimate or underestimate body fatness in some individuals since it does not take into consideration an individual's muscle or bone mass. The clinical correlation of BMI has not been validated in some subpopulations; therefore, BMI should not be used as the sole criteria for making health recommendations.	2016-2018 for current definition; 2010-2015 for previous definition.	Prior to 2016, BMI was calculated with the same method using self-reported weight and height from the MIHA survey.	Starting in 2016, the indicator is not comparable with prior years.
  Obese before pregnancy	Body Mass Index (BMI) was calculated from weight and height reported on the birth certificate. BMI of 30 or greater is classified as obese. BMI was calculated only for birthing people reporting height within 48-83 inches and weight within 75-399 pounds. BMI values outside of 13-69.99 are excluded. BMI may overestimate or underestimate body fatness in some individuals since it does not take into consideration an individual's muscle or bone mass. The clinical correlation of BMI has not been validated in some subpopulations; therefore, BMI should not be used as the sole criteria for making health recommendations.	2016-2018 for current definition; 2010-2015 for previous definition.	Prior to 2016, BMI was calculated with the same method using self-reported weight and height from the MIHA survey.	Starting in 2016, the indicator is not comparable with prior years.
  Inadequate weight gain during pregnancy	Adequacy of total weight gained during pregnancy, using pre-pregnancy BMI based on the birth certificate, was based on the National Academies of Science, Engineering and Medicine guidelines and restricted to birthing people who delivered at 37-42 weeks gestation, singletons and twins, prenatal weight gain within 0-97 pounds, height within 48-83 inches, pre-pregnancy weight within 75-399 pounds and BMI values within 13-69.99. See National Academies of Science, Engineering guidelines for more detail. BMI may overestimate or underestimate body fatness in some individuals since it does not take into consideration an individual's muscle or bone mass. The clinical correlation of BMI has not been validated in some subpopulations; therefore, BMI should not be used as the sole criteria for making health recommendations.	2016-2018 for current definition; 2010-2015 for previous definition.	Prior to 2016, pre-pregnancy BMI was calculated with the same method using self-reported weight and height from the MIHA survey.	Starting in 2016, the indicator is not comparable with prior years.
  Excessive weight gain during pregnancy	Adequacy of total weight gained during pregnancy, using pre-pregnancy BMI based on the birth certificate, was based on the National Academies of Science, Engineering and Medicine guidelines and restricted to birthing people who delivered at 37-42 weeks gestation, singletons and twins, prenatal weight gain within 0-97 pounds, height within 48-83 inches, pre-pregnancy weight within 75-399 pounds and BMI values within 13-69.99. See National Academies of Science, Engineering guidelines for more detail. BMI may overestimate or underestimate body fatness in some individuals since it does not take into consideration an individual's muscle or bone mass. The clinical correlation of BMI has not been validated in some subpopulations; therefore, BMI should not be used as the sole criteria for making health recommendations.	2016-2018 for current definition; 2010-2015 for previous definition.	Prior to 2016, pre-pregnancy BMI was calculated with the same method using self-reported weight and height from the MIHA survey.	Starting in 2016, the indicator is not comparable with prior years.
  Food insecurity during pregnancy (previous)	Calculated from the modified U.S. Department of Agriculture (USDA) Food Security Module Six-Item Short Form and categorized as food secure (0-1) or food insecure (2-6). Responses with one or two missing values were imputed. See USDA guidelines (PDF) for more detail.	2010-2018	None ---	None ---
  Food insecurity during pregnancy	During pregnancy, sometimes or often: worried whether food run out before they got money to buy more or the food bought didn't last and they didn't have money to get more.	2019-2021	Prior to 2019, food insecurity was calculated from the USDA Food Security Module.	Starting in 2019, the indicator is not comparable with prior years.

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• Intimate Partner Violence (IPV)

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  Intimate Partner Violence (IPV)

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Physical IPV in the year before pregnancy	During the 12 months before pregnancy, respondent was pushed, hit, slapped, kicked, choked or physically hurt in any way by current or former partner.	2010-2011	None ---	None ---
  Physical or psychological IPV during pregnancy	During pregnancy, experienced any of the following: pushed, hit, slapped, kicked, choked or physically hurt in any way by current or former partner; frightened for safety of self, family or friends because of current or former partner's anger/threats; current or former partner tried to control most/all daily activities.	2012-2016; 2019-2021	Prior to 2012, IPV indicator measured physical IPV in the year before pregnancy; starting in 2017, psychological IPV was added.	The physical or psychological IPV during pregnancy indicator is not comparable to the physical IPV before pregnancy nor the physical, psychological, or sexual IPV during pregnancy indicators.
  Physical, psychological, or sexual IPV during pregnancy	During pregnancy, experienced any of the following: pushed, hit, slapped, kicked, choked or physically hurt in any way by current or former partner; frightened for safety of self, family or friends because of current or former partner's anger/threats; current or former partner tried to control most/all daily activities; forced into any type of unwanted sexual activity by current or former partner.	2017-2021	Prior to 2017, IPV indicator measured physical or psychological IPV during pregnancy; starting in 2017, sexual IPV was added.	In 2017, replaced previous Physical or psychological IPV during pregnancy indicator and is not comparable with prior indicators.

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• Mental Health

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  Mental Health

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Depression before pregnancy	Before pregnancy, told by a health care worker that they had depression.	2019-2021	None ---	None ---
  Prenatal depression symptoms (previous)	During pregnancy, experienced both of the following for two weeks or longer: felt sad, empty or depressed for most of the day; lost interest in most things she usually enjoyed.	2010-2015	None ---	None ---
  Prenatal depression symptoms	During pregnancy, always or often: felt down, depressed or hopeless, or had little interest or pleasure in doing things usually enjoyed.	2016-2021	Prior to 2016, the indicator was based on a different set of questions and defined as during pregnancy, experienced both of the following for two weeks or longer: felt sad, empty or depressed for most of the day; lost interest in most things she usually enjoyed.	In 2016, replaced the previous prenatal depression symptoms indicator and is not comparable with prior years.
  Postpartum depression symptoms (previous)	Since most recent birth, experienced both of the following for two weeks or longer: felt sad, empty or depressed for most of the day; lost interest in most things she usually enjoyed.	2010-2015	None ---	None ---
  Postpartum depression symptoms	Since most recent birth, always or often: felt down, depressed or hopeless, or had little interest or pleasure in doing things usually enjoyed.	2016-2021	Prior to 2016, the indicator was based on a different set of questions and defined as since most recent birth, experienced both of the following for two weeks or longer: felt sad, empty or depressed for most of the day; lost interest in most things she usually enjoyed.	In 2016, replaced previous postpartum depression symptoms indicator and is not comparable with prior years.

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• Hardships and Support During Pregnancy

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  Hardships and Support During Pregnancy

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Experienced two or more hardships during childhood	Composite indicator measuring two or more hardships experienced during the woman's childhood (from birth through age 13). Hardships included: a parent or guardian she lived with got divorced or separated; she moved because of problems paying the rent or mortgage; someone in her family went hungry because family could not afford enough food; her parent or guardian got in trouble with the law or went to jail; a parent or guardian she lived with had a serious drinking or drug problem; she was in foster care (removed from her home by the court or child welfare agency), and very often or somewhat often her family experienced difficulty paying for basic needs like food or housing.	2011-2015	None ---	None ---
  Had a lot of unpaid bills	During pregnancy, had a lot of bills couldn't pay.	2010	None ---	None ---
  Homeless or did not have a regular place to sleep	During pregnancy, did not have a regular place to sleep at night (moved from house to house) or was homeless (had to sleep outside, in a car or in a shelter).	2011-2021	None ---	None ---
  Moved	During pregnancy, moved to a new address for any reason.	2010	None ---	None ---
  Moved due to problems paying rent or mortgage	During pregnancy, had to move because of problems paying the rent or mortgage.	2011-2021	Prior to 2011, indicator measured whether a woman moved to a new address for any reason.	In 2011, replaced previous Moved indicator and is not comparable with prior years.
  Woman/Pregnant person or partner lost job	During pregnancy, lost job even though wanted to go on working, or partner lost their job.	2010-2021	None ---	None ---
  Woman/Pregnant person or partner had pay or hours cut back	During pregnancy, had pay or hours cut back, or partner had pay or hours cut back.	2011-2021	None ---	None ---
  Became separated or divorced	During pregnancy, became separated or divorced from partner.	2010-2021	None ---	None ---
  Had no practical or emotional support	During pregnancy, had neither someone to turn to for practical help, like getting a ride somewhere, or help with shopping or cooking a meal; nor someone to turn to if needed someone to comfort or listen to them.	2010-2021	None ---	None ---
  Often experienced racism over her/their lifetime	During lifetime, very or somewhat often has been discriminated against, prevented from doing something or hassled or made to feel inferior because of race, ethnicity or color.	2016-2021	None ---	None ---

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• Substance Use

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  Substance Use

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Any smoking, 3 months before pregnancy	During the three months before pregnancy, smoked any cigarettes on an average day.	2010-2021	None ---	None ---
  Any smoking, 1st or 3rd trimester	During the first or last three months of pregnancy, smoked any cigarettes on an average day.	2011-2012 for current definition; 2010 for previous definition.	In 2011, the following phrase in italics was added to the question on smoking during the first trimester of pregnancy: “During the first 3 months of your pregnancy (including before you knew you were pregnant for sure), how many cigarettes or packs of cigarettes did you smoke on an average day?  (A pack has 20 cigarettes.)"	Starting in 2011, the indicator is not comparable with prior years.
  Any smoking, 3rd trimester	During the last three months of pregnancy, smoked any cigarettes on an average day.	2013-2021	Prior to 2013, this indicator was combined with any smoking during the first trimester.	In 2013, this indicator replaced previous Any smoking, 1st or 3rd trimester indicator and is not comparable to prior years.
  Any smoking, postpartum	At the time of the survey, smoked any cigarettes.	2011-2021	None ---	None ---
  Any binge drinking, 3 months before pregnancy	During the three months before pregnancy, drank four or more alcoholic drinks in one sitting (within about two hours) at least one time.	2010-2021	None ---	None ---
  Any alcohol use, 1st or 3rd trimester	During the first or last three months of pregnancy, drank any alcoholic drinks in an average week.	2011-2012 for current definition; 2010 for previous definition.	In 2011, the phrase in italics was added to the question on drinking during the first trimester of pregnancy: “During the first 3 months of your pregnancy (including before you knew you were pregnant for sure), about how many drinks with alcohol did you have in an average week?"	Starting in 2011, the indicator is not comparable with prior years.
  Any alcohol use, 3rd trimester	During the last three months of pregnancy, drank any alcoholic drinks in an average week.	2013-2021	Prior to 2013, this indicator was combined with any alcohol use during the first trimester.	In 2013, replaced previous Any alcohol use, 1st or 3rd trimester indicator and is not comparable to prior years.
  Any cannabis use during pregnancy	During most recent pregnancy, used marijuana or weed in any way (like smoking, eating or vaping).	2016-2021	None ---	None ---

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• Pregnancy Intention and Family Planning

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  Pregnancy Intention and Family Planning

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Mistimed or unwanted pregnancy	Just before pregnancy, felt that they did not want to get pregnant then or in the future, or wanted to get pregnant later.	2011-2018	None ---	Starting in 2011, the indicator is not comparable with the unintended pregnancy indicator from prior years.
  Unsure of pregnancy intentions	Just before pregnancy, felt that they were not sure if they wanted to get pregnant.	2011-2018	None ---	None ---
  Postpartum birth control use	At the time of the survey, birthing person or partner was doing something to keep from getting pregnant. Birthing people who were currently pregnant or had a hysterectomy/oophorectomy are excluded from the denominator.	2013-2021 for current definition; 2011-2012 for previous definition.	Prior to 2013, definition excluded from the denominator those who were currently pregnant and who were not having sex at the time of the survey.	Starting in 2013, the indicator is not comparable with prior years.

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• Infant Sleep

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  Infant Sleep

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Placed infant on back to sleep	Put baby down to sleep on his or her back most of the time. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2010-2021	None ---	None ---
  Infant always or often shared bed	Baby always or often slept in the same bed with her or someone else. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2010-2011, 2013-2021	None ---	Question was not on the survey in 2012.

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• Breastfeeding Intention and Duration

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  Breastfeeding Intention and Duration

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Intended to breastfeed, before birth	Before delivery, planned to breastfeed only or to breastfeed and use formula. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2010-2021	None ---	None ---
  Intended to breastfeed exclusively, before birth	Before delivery, planned to breastfeed only. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2010-2021	None ---	None ---
  Ever breastfed	Any breastfeeding or feeding of breast milk by the birthing person, since birth. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2019-2021	None ---	None ---
  Any breastfeeding, 1 month after delivery	Fed infant breast milk for at least one month after delivery with or without formula, other liquids or food. Infant age is calculated from date of birth on the birth certificate. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2011-2021	The infant feeding questions changed in 2011.	Starting in 2011, the indicator is not comparable with prior years.
  Exclusive breastfeeding, 1 month after delivery	Fed infant only breast milk (no supplementation with formula, other liquids or food) for at least one month after delivery. Infant age is calculated from date of birth on the birth certificate. Birthing people whose infant did not reside with them at the time of the survey are excluded from the denominator.	2011-2021	The infant feeding questions changed in 2011.	Starting in 2011, the indicator is not comparable with prior years.
  Any breastfeeding, 3 months after delivery	Fed infant breast milk for at least three months after delivery with or without supplementing with formula, other liquids or food. Infant age is calculated from date of birth on the birth certificate. Birthing people whose infant did not reside with them or whose infant was not yet three months old at the time the respondent completed the survey are excluded from the denominator.	2011-2021	The infant feeding questions changed in 2011.	Starting in 2011, the indicator is not comparable with prior years.
  Exclusive breastfeeding, 3 months after delivery	Fed infant only breast milk (no supplementation with formula, other liquids or food) for at least three months after delivery. Infant age is calculated from date of birth on the birth certificate. Birthing people whose infant did not reside with them or whose infant was not yet three months old at the time of the survey are excluded from the denominator.	2011-2021	The infant feeding questions changed in 2011.	Starting in 2011, the indicator is not comparable with prior years.

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• Health Care Utilization

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  Health Care Utilization

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Had a usual source of pre-pregnancy care	Just before pregnancy, had a particular doctor, nurse or clinic they usually went to for health care.	2011-2018	Prior to 2011, the question included the phrase in italics: “Just before you got pregnant for your most recent birth."	Starting in 2011, the indicator is not comparable with prior years.
  Initiated prenatal care in 1st trimester	Had first prenatal care visit in the first three months or 13 weeks of pregnancy, not counting a visit for just a pregnancy test or a WIC visit.	2012-2021	In 2011, the phrases in italics were added to the questions: “Did you get any prenatal care during your most recent pregnancy?  (Please do not count a visit just for a pregnancy test or only for WIC, the Women, Infants and Children supplemental nutrition program.)" and “How many weeks or months pregnant were you when you had your first prenatal care visit? (Please do not count a visit just for a pregnancy test or only for WIC.)" In 2012, the filter question, “Did you get any prenatal care during your most recent pregnancy?" was dropped.	Starting in 2012, the indicator is not comparable with prior years.
  Received dental care during pregnancy	During pregnancy, visited a dentist, dental clinic or got dental care at a health clinic.	2012, 2015-2021	None ---	This indicator was reported as “had a dental visit during pregnancy" in 2009 and 2012 and is comparable to this indicator. Question was not on the survey 2013-2014.
  Received a Tdap vaccine during pregnancy	During most recent pregnancy, received a Tdap vaccination or shot.	2016-2021	None ---	None ---
  Received a flu shot during pregnancy	During most recent pregnancy, had a flu shot.	2016-2021	None ---	None ---
  Had a postpartum medical visit	Had a postpartum check-up for themself (the medical check-up 4-6 weeks after a giving birth).	2011-2021	None ---	None ---
  Mom or infant needed but couldn't afford care postpartum	Since her most recent birth, there was a time when she needed to see a doctor or nurse for her own medical care or for her infant but did not go because she could not afford to pay for it.	2010-2015	None ---	None ---

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• Public/Nutrition Program Participation

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  Public/Nutrition Program Participation

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Participated in WIC during pregnancy	WIC is the Special Supplemental Nutrition Program for Women, Infants and Children. Participation in WIC during pregnancy is based on self-report on the MIHA survey.	2010, 2013-2021 for current definition; 2012 for previous definition.	In 2012, participation in WIC during pregnancy was based on WIC client records obtained from WIC Management Information System (WIC MIS) and linked to the MIHA survey.	This indicator was not published for 2011.
  Received CalFresh (food stamps) during pregnancy	CalFresh, formerly known as food stamps, is the California Supplemental Nutrition Assistance Program.	2011-2021	Prior to 2011, the question did not include the phrase “(also called CalFresh benefits)".	Starting in 2011, the indicator is not comparable with prior years.

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• Health Insurance Coverage

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  Health Insurance Coverage

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Pre-pregnancy/ postpartum insurance	During the month before pregnancy/at the time of the survey, had Medi-Cal or a health plan paid for by Medi-Cal; private insurance through their or their husband's/partner's job, their parents or purchased directly; or was uninsured. Those with both Medi-Cal and private insurance were categorized as Medi-Cal.	2011-2021 for current definition; 2010 for previous definition.	Starting in 2011, women with “Other" insurance, such as military, Indian Health Service, Medicare or international, are not shown; the 2010 indicator combined the “Other" and “Private" insurance categories; and women were asked to provide the name of their health insurance plan, which was used to categorize insurance with greater precision.	Starting in 2011, the indicator is not comparable with prior years.
  Prenatal insurance	During pregnancy had one of the following to pay for prenatal care: Medi-Cal or a health plan paid for by Medi-Cal; private insurance through their or their husband's/partner's job, their parents or purchased directly; or was uninsured. Those with both Medi-Cal and private insurance are categorized as Medi-Cal.	2011-2021 for current definition; 2010 for previous definition.	Starting in 2011, women with “Other" insurance, such as military, Indian Health Service, Medicare or international, are not shown; the 2010 indicator combined the “Other" and “Private" insurance categories; and the prenatal insurance question changed in order to distinguish between Medi-Cal and a plan paid for by Medi-Cal, as well as to identify how women obtained private insurance. Women also were asked to provide the name of their health insurance plan, which was used to categorize insurance with greater precision.	Starting in 2011, the indicator is not comparable with prior years.
  Had any gaps in insurance during pregnancy	During pregnancy, had no health insurance plan at all to pay for prenatal care or had one or more periods without health insurance coverage.	2016-2021	None ---	None ---
  Infant health insurance	Infant had Medi-Cal or a health plan paid for by Medi-Cal; private insurance through parent's job or purchased directly; or was uninsured.	2011-2021 for current definition; 2010 for previous definition.	Starting in 2011, infants with “Other" insurance, such as military, California Children's Services, Indian Health Service or Medicare, are not shown; the 2010 indicator combined the “Other" and “Private" insurance categories; and women were asked to provide the name of their infant's health insurance plan, which was used to categorize insurance with greater precision. Women whose infant did not reside with them at the time of the survey are excluded from the denominator.	Starting in 2011, the indicator is not comparable with prior years.

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• Demographics

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  Demographics

  Indicator	Definition	Years Available	Change in Definition	Comparability
  Age	See Age subgroup definition.	2010-2021	None ---	None ---
  Education	See Education subgroup definition.	2010-2021	None ---	None ---
  Household income	See Household Income subgroup definition.	2010-2021	None ---	None ---
  Language spoken at home	Usually speaks English or English and Spanish equally; Spanish; an Asian; or other language at home. (If more than one language spoken, the one used most often).	2010-2021	None ---	None ---
  Marital status	At the time of birth, birthing person was married or living together as married (married or living with someone like they were married, but not legally married); or unmarried (single [never married], separated, divorced, or widowed)	2019-2021 for current definition; 2010-2018 for previous definition	Prior to 2019, unmarried category included those who were living with someone like they were married, but not legally married.	one Starting in 2019, the indicator 'Unmarried' is not comparable with prior years.
  Born outside the U.S.	Birthing parent's place of birth not in the U.S., reported on the birth certificate.	2010-2021	None ---	None ---
  Neighborhood Poverty	See Neighborhood Poverty subgroup definition.	2019-2021	None ---	None ---
  Lives in a high poverty neighborhood	Lives in a neighborhood, as defined by census tract of the residence reported on the birth certificate, in which 30% or more of residents are living below the federal poverty threshold. The estimated percentage of residents below poverty by census tract is obtained from American Community Survey 5-year estimates from the most recent year. Birth certificate and American Community Survey data are linked.	2016-2018 for current definition; 2013-2015 for previous definition.	Prior to 2016, high poverty neighborhood was defined as 20% or more of residents living below the federal poverty threshold.	Starting in 2016, indicator is not comparable to prior years.
  Race/Ethnicity	See Race/Ethnicity subgroup definition.	2010-2021	None ---	None ---
  Total Live Births	See Total Live Births subgroup definition.	2010-2021	None ---	None ---

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MIHA County-Level Data Availability

For the data years 2013-2021, Maternal and Infant Health Assessment (MIHA) county-level data are available for the top 35 counties with the largest numbers of births. 

MIHA Regions of California

Data Annotation and Suppression Criteria

The current MIHA data suppression criteria require estimates to be suppressed when:

• the sample numerator is less than 5,
• the number of women/birthing individuals in the population of interest (population denominator) is less than 100,
• the relative standard error (RSE) is greater than 50%, or
• a measure has been determined to address a sensitive topic and the prevalence is greater than 80% and the unweighted population divided by the weighted population is greater than 50%.

Additionally, estimates are annotated and users are warned to interpret with caution if the RSE is between 30% and 50%. The RSE is a commonly used measure of reliability, or precision, of survey estimates and is calculated using the following formulas:

For estimates with a prevalence ≤ 50%:  

Standard error ÷ estimate

For estimates with a prevalence > 50%:

Standard error ÷ (1-estimate)

Some MIHA publications using data from 2010-2012 used a previous set of suppression criteria in which estimates were suppressed when the number of events (sample numerator) was less than 10. 

Weighting Methods

Sampling weights are created in MIHA to account for the stratified design, oversampling of specific groups, non-response among the birthing people sampled and non-coverage of women/birthing people who could not be sampled because their births were not in the sampling frame. When the final MIHA sample is weighted each year, it is designed to be representative of all individuals who delivered live-born infants in California during the calendar year in which the survey was conducted and who met other criteria, including those who were California residents, at least 15 years of age, and had a singleton, twin, or triplet birth. Although MIHA data are weighted to the entire birthing population, minus exclusions, the survey is only administered in English and Spanish, and results may not be generalizable to birthing people who speak other languages. The population represented by MIHA is referred to as the “target" population and is defined using the annual birth file, which is the final compilation of California birth data released annually by the Center for Health Statistics and Informatics (CHSI). From 1999 to 2017, this file was the Birth Statistical Master File (BSMF) and starting in 2018, it is the California Comprehensive Master Birth File (CCMBF).

The MIHA survey design allows for oversampling of certain groups, meaning their probabilities of selection were greater than the proportions of births they represented in the state. This ensures that enough respondents participate in the survey to allow for analysis. These oversamples have included American Indian/Alaska Native women (2012-2015), Black women (all years), WIC-eligible women not participating in the WIC program (2010-2012), those with a preterm birth (2016 and later), the 20 counties with the most births (2010-2012), and the 35 counties with the most births (2013 to 2021).

Every MIHA respondent is assigned a survey weight, which indicates the number of similar birthing people in California that they represent. Starting in 2010, this State Weight has consisted of 4 components (see below) calculated within strata. Additional steps have been added in subsequent years to create a Final Weight and improve the ability of the sample to represent the target population. Starting in 2011, raking (see details below) was added to the weighting process to adjust the State Weights to more accurately represent the annual birth file, particularly at the county level. Starting in 2013, trimming of weights (see details below) was implemented to reduce the influence of excessively large survey weights. These methods of raking and trimming continue to be used in all MIHA publications since 2013.

Calculation of the State Weight

The components of the State Weight are as follows: 

Non-Coverage Weight

The non-coverage weight accounts for differences between the frame from which the sample is drawn and the target population to which generalizations are made. The MIHA sample is drawn from birth certificate data for births occurring from February through May of each year, which is referred to as the "sampling frame." In 2020, due to the COVID-19 pandemic, the sampling frame was comprised of births occurring from March through June. Birth certificate data files from which the MIHA sample is drawn are provided in monthly batches by the CHSI. The non-coverage weight accounts for the difference between the number of births in the sampling frame and the number in the calendar year. The non-coverage weight also accounts for changes that might be made to the birth file after the sample is taken (e.g., births may not be in the frame files for sampling if they are reported late, but these late reported births are eventually included in the annual birth file). The non-coverage weight is defined, within stratum  S, as:

Number in the Target Population _S ÷ Number in the Sampling Frame _S

Inverse of Sampling Fraction

The sampling fraction is the probability of selection, or the ratio of the number of birthing people sampled to the number of birthing people in the sampling frame. Therefore, the inverse of the sampling fraction within stratum S is:

Number in the Sampling Frame _S ÷ Number Sampled _S

Non-Response Weight

This weight adjusts for non-response to the survey by birthing people who were sampled. The non-response weight is calculated within stratum S as:

Number Sampled _S ÷ Number of Respondents _S

Post-stratification Weight for Non-response (Propensity Score Adjustment)

The non-response weight described above accounts for non-response on factors used to define the strata (e.g., Black race, term or preterm birth, and county/region of residence). Additional individual-level factors may also predict whether a birthing person is likely to respond to the MIHA survey. Therefore, another adjustment for non-response is calculated to make the MIHA survey more representative of the target population from which the sample is taken. The probability of responding (versus not responding) is calculated using a geographically stratified logistic regression model of all sampled individuals. Variables in the logistic regression model come from the annual birth file and include maternal race/ethnicity, US or foreign birthplace, age, education, reported principal source of delivery payment, total children born alive, month prenatal care began, WIC participation, and term or preterm birth. A predicted probability (p) of being a respondent, or propensity score, is output for every individual sampled. The score is then rescaled, which means that p is multiplied by a constant factor for all respondents, so that the sum of p over all respondents now adds to the number of respondents. Starting in 2014, the post-stratification weight is capped at the 99th percentile of the post-stratification weight for each year.

Formula for State Weight

The State Weight is calculated using the four components defined above:

NON-COVERAGE * INVERSE SAMPLING FRACTION * NON-RESPONSE * POST-STRATIFICATION

Adjustments to Create the Final Weight 

Raking Survey Weights (or Iterative Proportional Fitting)

The State Weight alone produces weighted data that are very close to the data from the annual birth file at the state level and for most counties/regions. However, there are some remaining discrepancies between the weighted MIHA data and the annual birth file within subgroups of birthing individuals and at the county and regional levels. Raking the State Weights produces estimates that are closer to those of the annual birth file for subgroups, and at the county and regional level.

Raking is a process by which the weighted prevalence of a selected variable is aligned with the known prevalence in a target population. In MIHA, the State Weights are raked so that weighted birth certificate variable estimates reflect those of the annual birth file as closely as possible at the level of the respondent's sampling region (county or group of counties).

Raking is conducted over a series of predetermined variables, one at a time, in an iterative process. Raking variables include maternal age, race/ethnicity, nativity, prior cesarean section (2010-2012), low birth weight, preterm birth, prior live births, delivery payer, delivery method, BMI before pregnancy (2013 forward), education (2013 forward), and WIC participation (2017 forward). The weight assigned to each birthing individual who falls in category C of raking variable V is multiplied by a factor of:

Number in the Target Population vc ÷ Weighted Number of MIHA Respondents vc

The first adjustment is made to the State Weight calculated in the previous section. This results in a different weight value, which is adjusted using the next raking variable and the process continues for each variable. After this is done for all desired variables, the data are checked to ensure the percentages for each raking variable are as close as possible to those of the annual birth file within the sampling region or group. If results can be adjusted to be more similar to those of the annual birth file, the process starts again with the first raking variable, using the weight from the previous iteration. After the raking process is complete, the resulting weight is rescaled (i.e., multiplied by a constant factor), so that the sum of the raked weights over all respondents adds to the number of people in the annual birth file who meet MIHA's inclusion criteria in that county/region. 

Trimming Survey Weights

The raked weights are trimmed to reduce the influence of excessively high individual weights. Weights within strata identified as having excessively large weights are trimmed at the third standard deviation (99.73^rd percentile), and weights are constrained to a fixed range of the original State Weight. Raked and trimmed weights are rescaled so that totals reflect county birth totals in the annual birth file.

After raking and trimming, differences between county-level and regional-level MIHA data and the annual birth file are small. Very few of the estimates in the largest  counties are greater than three percentage points different from those in the annual birth file after raking. Differences between MIHA and the target population are sometimes greater in smaller sampling regions than in counties that have more births. ​