Pregnancy Data from CPRD and HES

CPRD is a database of routinely collected, anonymised primary care health records for over 15 million patients, representing the UK population in age, sex, and ethnicity.18 CPRD comprises records of consultations, diagnoses and symptoms, prescriptions, tests, referrals to and feedback from secondary care, health‐related behaviours, and all additional care administered as part of routine general practice. In the United Kingdom, general practitioners (GPs) are the main point of contact for nonemergency health issues, including pregnancy. Thus, CPRD is a rich source of pregnancy data relating to antenatal and postnatal care and pregnancy outcomes. A practice‐specific family number enables mother‐infant pairs to be algorithmically linked (the CPRD Mother‐Baby link). Patients from 56% of CPRD GOLD practices can be linked to additional datasets, including Hospital Episode Statistics (HES), which comprises records of all patient care delivered by NHS hospitals in England, including maternity data. We used CPRD GOLD primary care data to generate the Pregnancy Register and linked HES data to validate it. The International Scientific Advisory Committee (ISAC)‐approved protocol for this study (ref 11_058) is provided in the Supporting information.