**Question:** Which of the following is true about vasa previa except?

A. Vasa previa is a rare complication of pregnancy where the fetal vessels (umbilical cord and/or fetoplacental vessels) protrude through the cervix into the vagina.
B. Vasa previa is a common condition affecting most pregnant women.
C. Vasa previa is a benign condition with no clinical significance for the fetus or mother.
D. Vasa previa is always diagnosed preoperatively during routine prenatal ultrasound examination.

**Correct Answer:** B. Vasa previa is a common condition affecting most pregnant women.

**Core Concept:** Vasa previa is a rare but serious obstetric complication, characterized by the accidental exposure of fetal vessels (umbilical cord and fetoplacental vessels) through the cervix into the vagina. This condition is extremely uncommon and should be differentiated from other, more common, pregnancy complications.

**Why the Correct Answer is Right:** Vasa previa is not a common condition, affecting only a small percentage of pregnant women. It is characterized by the accidental exposure of fetal vessels through the cervix into the vagina. The correct answer (A) highlights the rarity of this complication and emphasizes the importance of recognizing its clinical implications.

**Why Each Wrong Option is Incorrect:**

A. Although the description of vasa previa is accurate, it is not specific to option A. The statement "Vasa previa is a rare complication of pregnancy where the fetal vessels protrude through the cervix into the vagina" is more general and does not differentiate option A from the other options.

B. This option incorrectly states that vasa previa is common, which contradicts its rarity. In reality, vasa previa is a rare complication that should be distinguished from other, more common pregnancy complications.

C. Vasa previa is not a benign (harmless) condition. It is a serious complication with significant fetal and maternal risks, emphasizing the need for early recognition and management.

D. The statement "Vasa previa is always diagnosed preoperatively during routine prenatal ultrasound examination" is incorrect. Vasa previa diagnosis relies on a combination of clinical suspicion, vaginal bleeding, and ultrasound findings, as it may not be detected during routine prenatal ultrasound. Accurate vasa previa diagnosis requires careful clinical assessment and a high index of suspicion, especially in cases of abnormal vaginal bleeding during pregnancy.

**Clinical Pearl:**

Recognizing the rarity and serious nature of vasa previa is crucial for appropriate management. Vasa previa does not typically present during routine prenatal ultrasound examination, as it may be missed unless a high index of suspicion is maintained. Early detection and management of vasa previa are essential to minimize maternal and fetal morbidity and mortality risks. Clinical suspicion combined with abnormal vaginal bleeding in pregnancy is crucial for the diagnosis of vasa previa.