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Question 733
Obstetric infection → Viral
Classification
Question
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Varicella immunity in an immunosuppressed pregnant woman
Question Stem
An immunosuppressed pregnant woman has significant exposure to chickenpox. She recalls definite chickenpox in childhood and her VZV IgG concentration is 120 mIU/ml. Which interpretation is most appropriate?
Options
A
Her childhood history alone proves immunity and no laboratory assessment is relevant
B
Any detectable VZV IgG excludes the need for post-exposure prophylaxis
C
The threshold is 100 mIU/ml, so she requires no prophylaxis
D
Because she is immunosuppressed, previous infection may not be sufficient evidence of immunity and PEP should be offered at a VZV IgG level below 150 mIU/ml
E
Pregnancy itself requires VZIG irrespective of VZV IgG concentration
Explanation
When a pregnant woman is immunosuppressed for a reason other than pregnancy, a history of previous chickenpox, shingles or vaccination may not provide sufficient evidence of immunity. Serum VZV IgG should therefore be measured. In this group, PEP should be offered if VZV IgG is negative or below 150 mIU/ml. A result of 120 mIU/ml therefore meets the guideline criterion for PEP.
Option Validity
A) previous infection alone may not establish immunity in an immunosuppressed woman.
B) the guideline specifies a quantitative threshold in this group.
C) the immunosuppressed threshold is higher than 100 mIU/ml.
E) prophylaxis is determined by susceptibility and significant exposure, not pregnancy alone.
Further Reading
RCOG Green-top Guideline No. 13, Chickenpox in Pregnancy, section 4.3.