Vasa Previa: Prenatal Diagnosis and the Rationale Behind Using a 5 cm Distance from Internal Os

Area of Science:

• Maternal-Fetal Medicine
• Diagnostic Ultrasound
• Obstetrics

Background:

• Vasa previa diagnosis impacts perinatal outcomes, with prenatal detection and planned cesarean delivery significantly improving survival rates.
• Current ultrasonographic definitions for vasa previa lack universal consensus, particularly regarding the safe distance of fetal vessels from the cervical internal os for recommending vaginal delivery.
• Existing 2 cm cut-off is considered suboptimal, as cervical dilation can place fetal vessels within a 5 cm radius at risk.

Purpose of the Study:

• To address the lack of a universally accepted ultrasonographic definition for vasa previa.
• To determine a revised, more conservative distance from the cervical internal os for defining vasa previa.
• To improve perinatal outcomes by refining diagnostic criteria and delivery recommendations.

Main Methods:

• Review of existing literature and societal guidelines on vasa previa diagnosis and management.
• Analysis of case reports and evidence concerning perinatal deaths related to unprotected fetal vessels.
• Expert consensus on ultrasonographic measurement and risk assessment in pregnancies with vasa previa.

Main Results:

• A 2 cm distance from the internal os is insufficient to guarantee fetal vessel safety during labor.
• Complete cervical dilation poses a risk to fetal vessels within a 5 cm radius of the internal os.
• Evidence suggests perinatal deaths occur with unprotected vessels located beyond the 2 cm threshold.

Conclusions:

• A more conservative ultrasonographic definition for vasa previa, encompassing fetal vessels within 5 cm of the internal os, is imperative.
• Implementing this revised definition can enhance prenatal diagnosis and guide safer delivery decisions.
• Adopting a 5 cm cut-off is crucial for improving perinatal outcomes in pregnancies complicated by vasa previa.