**4. Vasa praevia**

Vasa praevia is a rare condition, in which the fetal blood vessels traverse the lower uterine segment in advance of the presenting part, unsupported by either the umbilical cord or placental tissue (e.g., **Figure 4**). This pathologic structure can cause fetal blood loss, with significant neonatal morbidity or death in case of spontaneous rupture of membranes or amniotomy. Also, fetal heart decelerations and bradycardia can occur if compression of these vessels appears, due to the presenting part [20]. This condition is encountered in 1:2500–5000 pregnancies [21]. The prenatal diagnosis is made with a high accuracy by ultrasound, with a sensitivity of 100% and a specificity

**Figure 4.** Ultrasound color Doppler image showing vasa praevia.

of 99–99.8%, if transvaginal color Doppler examination is used [20]. If unrecognized before the onset of labor, the fetal mortality rate ranges between 22.5 and 100% [22]. To improve the prenatal diagnosis, the prenatal ultrasound form should include a standard evaluation of the umbilical cord insertion site. However, some researchers demonstrated that general screening for vasa praevia is not cost-effective and is not advised [23]. There are recent reports of two main associations: velamentous insertions and vessels crossing between lobes in succenturiate or bilobate placentas [24]. Besides these strong risk factors, others include placenta praevia and conception by assisted reproductive technologies. If diagnosed with vasa praevia, elective Cesarean delivery should be proposed at 35–36 weeks [25]. Others prefer a scheduled Cesarean section at 37–38 weeks or when fetal lung maturation has been confirmed [26, 27]. The Canadian guidelines for the management of prenatally diagnosed vasa praevia include elective Cesarean section prior to the onset of labor. Also, as premature delivery is most likely, consideration should be given to administration of corticosteroids at 28–32 weeks (to promote fetal lung maturation), and hospitalization at about 30–32 weeks is advisable. Continuous electronic fetal heart rate monitoring and a rapid biochemical test for fetal hemoglobin can be considered, and if any of the above tests are abnormal, emergency Cesarean section should be performed [28]. Overall, physicians must be vigilant whenever amniotomy is performed as not all cases of vasa praevia are diagnosed antenatally. Any case of suspicion should benefit of immediate delivery, to avoid fetal shock or demise [22].
