Establishing the QResearch Pregnancy Register in the QResearch® database: methods and cohort description

Abstract Electronic health records can be used to facilitate research in pregnancy. This work describes the construction of a novel algorithm to create a unified pregnancy cohort in the QResearch database, during the initial phases of the COVID-19 pandemic, for England. National GP records in the QResearch® database were linked to patient-level data from Hospital Episode Statistics (HES) datasets. Females aged 15-50 years with a pregnancy recorded between December 2020 and September 2022 were included. Pregnancy (delivery/loss) episodes were identified and cohort demographics reported using a three-stage algorithm. 266,758 women with 279,027 pregnancies were identified. 232,673 pregnancies (83%) resulted in a delivery (99.6% live births and 0.4% stillbirths). 46,354 (17%) pregnancies resulted in a pregnancy loss. Pregnancy losses were highest amongst those of Caribbean (23.1%; n=781) ethnicity and lowest in those of Pakistani ethnicity (14.4%, n=1,579). The QResearch Pregnancy Register offers a useful and adaptable resource for future research on pregnancy exposures, outcomes, and events.