Patient population
In this prospective, diagnostic observational study, pregnant women who were admitted to our perinatal center for perinatal management between March 2019 and February 2020 were enrolled. Placental ultrasound evaluation using SMI was performed during pregnancy every 1–2 weeks. Therefore, the SMI findings in the present analysis were of those within 1–2 weeks before delivery. The findings on SMI were compared to those of the placenta submitted for pathological examination.