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Question 737
Obstetric infection → Viral
Classification
Question
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Risk of fetal varicella syndrome before 20 weeks
Question Stem
A woman develops confirmed chickenpox at 17 weeks of gestation and asks about the absolute risk of fetal varicella syndrome. Which estimate from pooled cohort data is most appropriate?
Options
A
Approximately 0.1%
B
Approximately 0.9%
C
Approximately 5%
D
Approximately 10%
E
Approximately 20%
Explanation
Pooled data from nine cohort studies identified 13 cases of fetal varicella syndrome among 1423 maternal chickenpox infections occurring before 20 weeks, an incidence of approximately 0.91%. The risk was lower in the first trimester at approximately 0.55%. FVS has nevertheless been reported following maternal infection as late as 28 weeks, so it is not confined to infection before 20 weeks.
Option Validity
A) this substantially underestimates the pooled incidence before 20 weeks.
C) 5% is considerably higher than the observed pooled incidence.
D) the absolute risk is far below 10%.
E) the pooled data do not support a risk approaching 20%.
Further Reading
RCOG Green-top Guideline No. 13, Chickenpox in Pregnancy, section 6.1.