Methods
Study design and participants
This study was designed as an observational cohort based on real-world data in two centers from March 2016 to December 2018. Pregnant women with twins who ‘booked’ at the First Affiliated Hospital of Chongqing Medical University were routinely offered prophylaxis with low-dose aspirin (LDA group) before 16 weeks of gestational age and those recruited from Chongqing Health Center for Women and Children were not required to take aspirin and regarded as the control group (NC group). This difference was based upon clinician preference at the two institutions. In the LDA group, participants were administered aspirin from the day when registered. Aspirin was taken at the dose of 100mg per night from recruitment until 35 weeks of gestation age. Inclusion criteria were: Twin pregnancies were diagnosed by ultrasound in the first visit. Those who did not start their first antenatal care in the two centers but delivered in these 2 hospitals were excluded in the final analysis due to incomplete records of prior medications. Pregnant women were asked to have a visit every 2 weeks before 28 weeks of gestational age, and every 1 week when the gestational week was over 28.
Data collection
All pregnant patient clinical, demographic, neonatal assessments, and outcomes data during pregnancy and at delivery were recorded in the Case Report Form (CRF). All the information was concurrently recorded in both Hospital Information Systems (HIS) and Cohort Management Systems. According to the medical records, each participant in the LDA group was confirmed to have an over 90% drug compliance.