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.