Normal fetal vessels travel in the umbilical cord surrounded by thick, gelatinous tissue (ie, Wharton jelly) that protects them. In contrast, vasa previais an aberrant condition in which the fetal vessels overlie the cervix, surrounded only by thin fetal membranes, making them prone to tear with rupture of membranes or contractions.
| Definition | • Fetal vessels overlying the cervix surrounded only by thin fetal membranes. the location and lack of Wharton jelly make them prone to tear with ROM or contractions |
|---|---|
| Risk factors | • Placenta previa |
| • Multiple gestations | |
| • In vitro fertilization | |
| • Succenturiate placental lobe | |
| Clinical presentation | • Painless vaginal bleeding with ROM or contractions |
| • FHR abnormalities (eg, bradycardia, sinusoidal pattern) | |
| • Fetal exsanguination & demise | |
| Management | • Emergency cesarean delivery |
Sinusoidal tracings are a category III tracing and are considered ominous because they are associated with severe fetal anemia.
diagnosed on fetal anatomy ultrasound at 18-20 weeks gestation, and patients normally require third-trimester, inpatient management to monitor for acute changes that require immediate delivery and early planned cesarean delivery at 34-35 weeks gestation (ie, prior to the onset of contractions or membrane rupture). However, vasa previa may be clinically diagnosed when patients present with rupture of membranes accompanied by painless, minimal vaginal bleeding that primarily reflects fetal blood loss from a torn fetal vessel. Vaginal bleeding is minimal because total fetal blood volume is low (~250 mL, or 1 cup); however, hypotension from fetal bleeding leads to fetal heart rate abnormalities (eg, bradycardia, sinusoidal pattern) and rapid (eg, within minutes) fetal exsanguination and **demise (**Doppler ultrasound is unable to detect fetal heart tones)
Vasa previa and rupture of membranes likely has a ruptured fetal vessel, as evidenced by the leakage of blood-tinged vaginal fluid and fetal bradycardia. This obstetric emergency requires immediate delivery. Because vaginal delivery can cause further fetal vessel tearing and fetal compromise, induction of labor is contraindicated.
(Choice C) Patients with prior cesarean deliveries are at increased risk for placenta previa, which can also present with painless vaginal bleeding. However, bleeding from placenta previa is primarily maternal blood loss and, therefore, usually heavy and persistent rather than minimal and transient. In addition, signs of maternal hemorrhagic shock (eg, hypotension, tachycardia) are typically present prior to severe fetal compromise.