Pre‐pregnancy Cardiovascular Health and Adverse Pregnancy Outcomes After Frozen Embryo Transfer: A Retrospective Cohort Study - Fengyi Ren; Wen Zhang; Mengyao Qin; Xin Liu; Zixuan Zhang; Fei Zhao; Lei Sheng; Ling Geng; Xinxia Chen (Paediatric and Perinatal Epidemiology, 2026)