EMQ — Extended Matching Question · Review
Question 756
Obstetric infection → Viral
Classification
Question
EEMQQuestion Header
Select the single most appropriate interpretation and counselling.
Question Stem
A woman had chickenpox at 17 weeks. After recovery she undergoes detailed fetal ultrasound, which is normal. Following counselling, amniotic-fluid VZV PCR is positive. She asks whether this proves that the fetus has fetal varicella syndrome.
Answer Bank
A
A positive PCR proves severe fetal varicella syndrome
B
A positive PCR mandates termination of pregnancy
C
A positive PCR has poor positive predictive value for fetal damage and does not by itself establish FVS
D
The PCR result excludes fetal infection
E
Ultrasound is irrelevant once PCR is positive
F
Positive PCR guarantees neonatal chickenpox
G
Immediate caesarean birth is required
H
Maternal VZIG will now eradicate fetal infection
Correct Answer
C. A positive PCR has poor positive predictive value for fetal damage and does not by itself establish FVS
Explanation
Amniotic-fluid VZV PCR has a strong negative predictive value but a poor positive predictive value for fetal damage. Women should therefore be counselled about the limitations as well as the risks and benefits of amniocentesis.
Option Validity
A) Detection of VZV DNA does not prove that fetal damage has occurred.
B) A positive PCR result alone is not an indication for termination.
D) A positive result cannot exclude fetal infection.
E) Ultrasound remains important in assessing fetal morphology.
F) Positive amniotic-fluid PCR does not guarantee clinical neonatal disease.
G) The result does not create an indication for immediate caesarean birth.
H) VZIG is PEP and does not eradicate established fetal infection.
Further Reading
RCOG Green-top Guideline No. 13. Chickenpox in Pregnancy.