Concept: Mother's Age at First Birth

Introduction

This concept provides information about the measure "mother's age at first birth" - the age of a mother when she gave birth to her first child. The concept describes the methodology used to calculate this measure following a SAS code example and identifies specific MCHP research that uses the measure, including a brief description of how it is used in the research and the outcomes associated with it.

Methodology

The following provides a summary description of a specific method used at MCHP to calculate the age of a mother at the time of birth of her first child. The methodology section includes a list of the data sets required to develop this measure and a descriptive summary of the steps taken using each of these data sets. The description follows the SAS code developed for calculating this measure and the SAS code is available in the SAS code and formats section below - (internal access only).

Usually this measure is restricted to Manitoba residents only and includes only live births; not stillbirths, abortions or miscarriages. The inclusion / exclusion criteria should be reviewed and verified before calculating the measure of mother's age at first birth. The methodology described in this concept only involves live births.

Data Sets

The following data sets are used in the algorithm to calculate the measure of mother's age at first birth:


• Hospital Abstracts data;
  
• Hospital Newborn to Mother Link Registry data; and
  
• Manitoba Health Insurance Registry data

How each of these data sets is used in this process is described below.

Step 1 - Using the Hospital Abstracts Data - Creating Recent Mother / Baby Linkage Records

The first step is to identify the cohort of mothers that will be included in the study. In the SAS code example, these come from the 2008/09 births available from the Hospital Abstracts data. Hospital births are identified by the presence of an ICD-10-CA diagnosis code of "Z37" in any of the 25 diagnoses fields. For earlier years (before 2004), hospital births are identified by an ICD-9-CM diagnosis code of "V27" in any of the 16 diagnosis fields. Additional data required from the hospital abstract record includes the mother's scrambled PHIN (Personal Health Identification Number), hospital admission and separation dates, and the mother's birthdate.

The next step is to create a SAS® format containing records with the mother's scrambled PHIN and birthdate. This step removes multiple births within the same year and multiple births on the same day (e.g.: twins, triplets) for the same mother. The result is one PHIN/birthdate record for each mother.

The next step is to retrieve the 2008/09 newborn hospital records and assign the mother's PHIN to the birth record. This will only include newborn records that have the mother's scrambled PHIN coded on them. The mother's birthdate can be added to the record using the format created above. If the hospital record is missing the newborn's birthdate, the admission date of the record is substituted for the newborn birthdate.

The file is then sorted by Mother's PHIN, the newborn's birthdate and PHIN, and any duplicate record combinations (on all three variables) are removed from the file.

Step 2 - Using the Hospital Newborn to Mother Link Registry Data

The next step is to use the Hospital Newborn to Mother Link Registry (HNMLR) data which contains historical data related to mothers and newborns that have already been identified from previous year's data, currently back to 1984/85.

Records in the HNMLR data should be reviewed for missing data. Records that have either a missing PHIN for the mother or newborn, or where the mother and newborn PHIN are the same, are removed. If the record is missing the mother's birthdate, then the format created above may contain the mother’s birthdate.

The file from the Hospital Abstracts data should be merged with the HNMLR file to create a complete hospital birth file. If the mother's birthdate is missing then the record is excluded. The complete hospital birth file is sorted by mother's PHIN and newborn PHIN and duplicate records are removed.

Mother's age at birth of the child is calculated using the SAS function YRDIF (years difference) and two variables: mother's birthdate and newborn's birthdate.

The complete hospital birth file is then sorted by mother's PHIN and age (in ascending order) and the first record is kept, identifying the mother's age at first birth. Any records where the mother's age is less than 12 years of age are excluded from the complete hospital birth file.

The resulting file provides preliminary information on the mother's age at first birth for mother's that gave birth in 2008/09, because this file only contains information related to births that occurred in a hospital.

Step 3 - Using the Manitoba Health Insurance Registry to Identify Additional Births

Not all births are recorded in the Manitoba hospital data. Some births take place in the home and some families who move into the province may already have children. A review of the Manitoba Health Insurance Registry data can assist in identifying the family structure in order to identify additional information on a women’s birth history. Relevant data includes records where the mother's PHIN is contained in the format created earlier, OR the mother is registered as a spouse (legal or common-law) or as a family head. Other relevant Registry data used in the algorithm includes registration start and end dates, insurance cancellation date and reason, scrambled PHIN, record type, Registration Number (REGNO) / (REGNO_CODE) and relationship to the family head. NOTE: Access to the Registry file is restricted.

Records can be excluded if a duplicate PHIN was issued, or the cancellation date is before the data acquisition date. Records indicating someone belonging to the military, an inmate of a federal institution, no longer a ward, or they cannot be located are updated so the end date of coverage equals the acquisition date.

Two SAS® formats are created. The first format identifies a mother belonging to a specific family at a particular point in time and contains a KEY - the REGNO and data acquisition date. The second format contains all the children belonging to a specific REGNO. This includes children identified as a child, step-child or incapacitated child, using the relationship code (RELCODE) values in the Registry file. A KEY is generated based on the children's REGNO and data acquisition date.

These two files are merged and those with the following conditions are retained in the file:


• children that have a birthdate before the end date of insurance coverage;
  
• if the mother is a family head, then dependent children and incapacitated children are included; or
  
• if the mother is a spouse, then all children including step-children are included.

The mother's age at child’s birth is calculated using the SAS function YRDIF (years difference) and two variables: mother's birthdate and child’s birthdate. If the mother's age is less than 12 years of age, the record is excluded. Duplicate records containing the same mother and child PHIN combinations are removed from the file.

A check is done to identify cases where the same child may be linked to more than one mother in the Registry file. If a case exists, this should be checked against data in the HNMLR data to determine who the mother was at the time of birth, and the record(s) that do not agree with this are removed from the file.

The file containing the registry data and the complete hospital birth file (created in step 2) are merged to create a file containing additional children attributable to a mother. This file is then sorted by mother's PHIN and age at birth (in ascending order) and the first record (earliest birth) is retained in the file, identifying the mother's age at first birth.

SAS Code

The three steps described above summarize the example SAS code that is provided in the SAS code and formats section below (internal access only).

MCHP Research and Mother's Age at First Birth

Along with other factors, mother's age at first birth is a strong predictor of various outcomes of children's health throughout their life. In general, the average age at which women give birth to their first child has increased in recent years and births to teenage mothers have decreased. Both of these trends correspond to an increase in age of first marriage.

Several deliverables published at MCHP focus on early child health and therefore the health and status of their mothers. The following sections summarize the ways that the measure of mother's age at first birth has been used in MCHP research and the findings of this research. Links are included to relevant sections in each publication.

1. Brownell et al. (2007)

In the deliverable Next Steps in the Provincial Evaluation of the BabyFirst Program: Measuring Early Impacts on Outcomes Associated with Child Maltreatment by Brownell et al. (2007), they investigated the relationship between mother's age at first birth and children going into care of Child and Family Services (CFS) and children receiving services from CFS. Mother's age at first birth, especially younger mothers, was found to be a significant predictor of children going into care and for children receiving services from CFS.

For more information on the percentage of infants given the BabyFirst screen (and the at-risk assessment) of different age at first birth categories, please see:


• Figure 3.6a: Percent Infants Given BabyFirst Screen by Maternal Age at First Birth, All Manitoba, and
  
• Figure 3.6b: Percent Infants Given BabyFirst Screen by Maternal Age at First Birth, Winnipeg Only

For more general information, please read section 3.3 Validity of the Babyfirst Screen in this deliverable.

2. Brownell et al. (2010)

In the deliverable Evaluation of the Healthy Baby Program by Brownell et al. (2010), they investigated the relationship between mother's age at first birth and receipt of the Healthy Baby Prenatal Benefit and participation in the Community Support Programs. The research found:


• as mother's age at first birth increases, the percent of expectant moms applying for the Healthy Baby Prenatal Benefit decreases - see Figure 3.8: Percent of Births by Healthy Baby Prenatal Benefit Application Type by Mother's Age at First Birth, 2004/05 - 2007/08
  
  
• almost half of mother's aged 19 and younger who apply for the Health Baby Prenatal Benefit are approved - see Figure 3.9: Percent of Births by Mother's Age at First Birth, by Healthy Baby Prenatal Benefit Application Type, 2004/05 - 2007/08
  
  
• mothers who were teens at first birth were more likely to participate in prenatal compared to postnatal Community Support Programs and made up 45.5% of those participating in prenatal Community Support Programs only. However, they made up only 29.7% of participants in pre- and postnatal programs and 17.5% of those participating only in postnatal programs - see:
  
  
  • Figure 3.16: Percent of Births by Community Support Program Participation by Mother's Age at First Birth, 2004/05 - 2007/08
    
  • Figure 3.17: Percent of Births by Mother's Age at First Birth, by Community Support Program Participation, 2004/05 - 2007/08
  
  For more information, please read Chapter 3: Who Participates in the Manitoba Healthy Baby Program in the deliverable.

3. Martens et al. (2010)

In the deliverable Profile of Metis Health Status and Healthcare Utilization in Manitoba: A Population-Based Study by Martens et al. (2010), they investigated the relationship between mother's age at first birth and teenage pregnancy, likelihood of breastfeeding, and complete immunizations. The research compared aggregate regions of Manitoba and the Metis versus all others. The research found:


• within the 15–19 year old age range, the older the teen, the more likely a teen pregnancy occurs;
  
• as the mother's age at first birth increases, the likelihood of her teenage daughter becoming pregnant decreases;
  
• the higher the maternal age at first birth, the greater the likelihood of breastfeeding a newborn; and
  
• for the Metis population only, the higher the mother’s age when she gave birth to her first baby, the more likely the child had two–year–old complete immunizations.

4. Jutte et al. (2010)

In the publication The ripples of adolescent motherhood: Social, educational, and medical outcomes for children of teen and prior teen moms by Jutte et al. (2010), the objective was to examine "medical, educational and social risks to children of teen mothers and children of nonadolescent mothers with a history of teen birth (prior teen mothers) and consider these risks at both the individual and societal level". The cohort included children in Winnipeg born and raised in Manitoba from 1979-1982 and 1984-85, and used different administrative data sets found in the MCHP Data Repository.

The results of this research found ... "For children of both teen and prior teen mothers, adjusted likelihoods of death during infancy, school-aged years, and adolescence were more than 2-fold higher than for other children. Risks for hospitalization, high hospital use, academic failure, and poor social outcomes were also substantially higher. At a societal level, only 16.5% of cohort children were born to teen and prior teen mothers. However, these children accounted for 27% of first-year hospitalizations, 34% of deaths (birth to 17 years), 30% of failures to graduate high school, 51% in foster care, 44% on welfare as young adults, and 56% of next-generation young teen mothers".

5. Brownell et al. (2012)

In the deliverable How are Manitoba's Children Doing? by Brownell et al. (2012), they investigated the relationship between mother's age at first birth and educational outcomes in Kindergarten, using the Early Development Instrument (EDI) as an assessment tool, and in grade 3 reading assessments. Maternal age at birth was used as one of several variables in the models to measure educational performance. The research found:


• children of mothers who were older at first birth were significantly related to better outcomes on Grade 3 reading.
  
• children of older mothers at first birth were also associated with better performance on the language and cognitive development domain on the EDI.

For more information, please read:


• the section titled Modeling of Successful Learning from Kindergarten to Grade 3 that describes how maternal age at first birth was used in the structured equation modelling (SEM) process of this research; and
  
• Chapter 5: Successful Learning for general measures of educational outcomes found in this research.

6. Brownell et al. (2015)

In the deliverable The Educational Outcomes of Children in Care in Manitoba by Brownell et al. (2015), they investigated the relationship between mother's age at first birth and children taken into care, children in families who have ever received services from Child and Family Services (CFS), and children neither in care nor who received services from CFS. The research found:


• children born to mothers whose first birth is during the teen years tend to have poorer outcomes than children born to mothers who were older when they started having children; and
  
• children who were in care are much more likely to have mothers who were younger at first birth than children who received services from CFS or children neither in care nor who received services from CFS.

For more information, please read the section titled Mother's Age at First Birth in the deliverable.

Cautions / Limitations

The following limitations / cautions should be considered when doing research into mother's age at first birth:


• births attributable to a mother less than 12 years old, or whose birth date cannot be found in the data should be excluded from analysis.
  
• usually, stillbirths or pregnancy outcomes other than a live birth (e.g.: abortion, miscarriage) would be excluded from this type of analysis.
  
• a child found through the Registry may not be a biological child of the mother (e.g.: adoption), but the Registry can be used to identify children born outside of the hospital, or before 1984/85, or belonging to a family when they move into the province. Whether to include these children in the algorithm are specific decisions that need to be made in each research project.
  
• the age of the mother can be calculated for "age at birth of a cohort child" or for "age at birth of first child", regardless of whether that child is in the cohort or not.