Introduction

This concept describes the methods used to develop a cohort to investigate the relationship between maternal adolescent childbearing and an older sister's teenage pregnancy on the likelihood of a younger daughter's/sister's teenage pregnancy. The concept includes information on how pregnancy was defined using administrative data, including the specific diagnostic and procedure/intervention codes; identifies the age range used in this research for determining teenage pregnancy; and briefly describes how sisters are identified from the administrative data. The concept also identifies the steps involved in developing the cohort for this research.

Information for this concept comes from the article, The impact of maternal adolescent childbearing and older sister's teenage pregnancy on a younger sister by Elizabeth Wall-Wieler, Leslie L. Roos, and Nathan C. Nickel. The article is published in the journal BMC Pregnancy and Childbirth, v. 16(1), 2016 and is copyrighted under the Creative Commons Attribution 4.0 International License.

Definitions

The following definitions were used in this research:

Pregnancy was defined from the Hospital Abstracts data as having at least one hospitalization with a diagnosis of:


• live birth - ICD-9-CM code V27; ICD-10-CA code Z37;
  
• missed abortion - ICD-9-CM code 632, ICD-10-CA code O02.1;
  
• ectopic pregnancy - ICD-9-CM code 633, ICD-10-CA code O00;
  
• abortion - ICD-9-CM codes 634-637 ICD-10-CA codes O03-O07; or
  
• intrauterine death - ICD-9-CM code 656.4, ICD-10-CA code O36.4;

or a hospitalization with at least one of the following procedures/interventions:


• surgical termination of pregnancy - ICD-9-CM codes 69.01, 69.51, 74.91; CCI codes 5.CA.89, 5.CA.90;
  
• surgical removal of extrauterine (ectopic) pregnancy - ICD-9-CM codes 66.62, 74.3; CCI code 5.CA.93;
  
• pharmacological termination of pregnancy - ICD-9-CM code 75.0; CCI code 5.CA.88; or
  
• interventions during labour and delivery - CCI codes 5.MD.5, 5.MD.60
  
  NOTE: The ICD-9-CM coding system was used to identify diagnoses and procedure codes for data from the beginning of the study to March 31, 2004. From April 1, 2004 to present, the ICD-10-CA coding system was used to identify diagnoses codes and the CCI was used to identify intervention codes. This is because of a change in coding systems in the Hospital abstracts data.

Teenage pregnancy was defined as having at least one pregnancy (see definition above) between the ages of 14 and 19 (inclusive). Pregnancies before the age of 14 were excluded due to low numbers and for comparability to other studies.

Children are linked to mothers using the Hospital Abstract birth record information, and sisters were defined as having the same biological mother. When a family had more than one younger sister (more than two daughters), one younger sister was randomly selected.

Cohort Development Process

The following steps / criteria were used to select the cohort for this study:


• First, select women born between April 1, 1979 and March 31, 1995 and were included in the Repository.
  
  
• Then, select only women who were born in Manitoba.
  
  
• Then, include only women who lived in Manitoba until their 20th birthday (they did not move out of Manitoba or die before their 20th birthday).
  
  
• Following this, select the women with no missing data. Missing data included:
  
  • Birth Weight,
    
  • birth order,
    
  • Family Structure History,
    
  • Mother's Age at First Birth,
    
  • Residential Mobility history,
    
  • family identifier, and
    
  • neighborhood Income Quintile. .
  
  
• Next, women who were the oldest sibling in the cohort were selected. This sibling had to be a female.
  
  
• Then, women who had at least one sister in the cohort were selected.
  
  
• Next, women who had no sisters that had a pregnancy before age 14 were selected. The selected women also had to have at least one older sister.
  
  
• Finally, in families that had more than two daughters, one younger sister per family was randomly selected.

The selection process resulted in a final cohort of 17, 115 women.

The steps above are adapted from Figure 1 in the on-line article. The figure illustrates the selection trajectory process for developing this cohort, and provides the number of cases that were included/excluded at each step.