Randomization and blinding
BLIND
The pregnant women were randomly divided into a control group and a nitroglycerin group at a 1:1 ratio by an independent researcher using numbered sealed envelopes. An independent researcher performed nitroglycerin injection or local anesthesia and was not involved in data collection. A doctor with much experience in vascular examinations performed the ultrasound examinations and was blind to the group allocation. The outcome assessor who was unaware of the group allocation evaluated the cross-sectional area and diameter of the radial artery according to ultrasonographic measurements. In addition, the included patients, surgical doctors, and data analysts were all blinded to the group assignments.