2.1 Data source
The data used in this study were from the Taiwan Maternal and Child
Health Database (TMCHD), which consists of four linked nationwide
databases, namely the National Health Insurance Research Database
(NHIRD), the Birth Certificate Application (BCA) database, Birth
Registration Database (BRD), and the National Register of Death (NRD) in
Taiwan.
The NHI (National Health Insurance) program was launched in Taiwan in
1995 and covers over 99% of the nation’s population of approximately 23
million residents, with medical claims data on all outpatients and
inpatients. Information regarding demographic data, dates of visits,
disease diagnoses, prescriptions, and medical orders are included in the
NHIRD. Information related to birth of children and nationality of
mother are included in the BCA database, whereas the NRD contains the
survival status of infants. Using the unique personal identification
numbers of residents in Taiwan, we were able to confirm the
relationships between parents and children through the BRD and link
individuals across the four databases. The diagnosis of diseases was
based on the International Classification of Diseases, 9th and10th Revision, Clinical Modification (ICD-9-CM andICD-10-CM ). The study was approved by the ethical review board of
Chung Shan Medical University Hospital.