Pathophysiology
Clinical meaning
Antepartum complications encompass a range of pregnancy-related disorders that threaten maternal and fetal well-being before the onset of labor. Understanding the underlying pathophysiology of the three most critical antepartum emergencies -- placenta previa, placental abruption, and preeclampsia -- is essential for practical nurses who must recognize warning signs and initiate timely interventions within their scope of practice. Placenta previa occurs when the placenta implants partially or completely over the internal cervical os rather than in the normal upper uterine segment. During normal implantation, the blastocyst embeds in the well-vascularized fundal region of the uterus where the endometrium (decidua) is thickest. In placenta previa, abnormal implantation in the lower uterine segment places the placenta directly over the cervix. As the lower uterine segment thins and stretches during the second and third trimesters, the placental villi are torn from the uterine wall, exposing the maternal blood sinuses at the implantation site. This results in painless, bright red vaginal bleeding that is the hallmark of placenta previa. The bleeding is painless because the placenta separates passively as the lower segment stretches -- there...