To clarify these issues, in the present work, we collected early-onset PE, early-onset PE complicated by the HELLP syndrome, and late-onset PE placental samples, and their well-matched control tissues, and systematically examined the expression of p21 (CDKN1A) and its family members p27 (CDKN1B) and p57 (CDKN1C) as well as their roles in normal pregnancy and hypertensive disorders. Here, CDKN1A is linked to HELLP syndrome.