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Measles exposure in pregnancy — MSRA MCQ

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HardInfectious DiseasesMeasles exposure in pregnancyMSRA

A 29-year-old woman who is 18 weeks pregnant contacts her GP after her 3-year-old nephew, whom she cares for daily, is diagnosed with PCR-confirmed measles. The child was unvaccinated and developed his rash 5 days ago. She spent more than 2 hours with him indoors 6 days ago, when he had fever, coryza and conjunctivitis but no rash. She was born in 1997 and has one documented MMR dose at age 14 months. She has no history of measles, is otherwise well and is not immunosuppressed. A local laboratory can return a measles IgG result within 4 hours, and HNIG can be obtained today if indicated. What is the most appropriate management today?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Request urgent measles IgG today and administer intramuscular HNIG today if the result is antibody negative

Explanation lettering: C = shown as A · A = shown as B · B = shown as C

This is a significant exposure: the child had primary measles and she had prolonged indoor contact during the infectious prodrome, which begins 4 days before rash onset. She is pregnant, born after 1990, and has received only one documented measles-containing vaccine; she therefore requires assessment of susceptibility rather than being presumed immune. For pregnant contacts with one previous measles-containing vaccine, UKHSA recommends urgent measles IgG testing and HNIG within 6 days of exposure only if measles antibody is negative. She is at the end of that window, but a same-day result is available, so empiric HNIG is not indicated. Equivocal measles IgG is treated as evidence of detectable antibody in this group and does not justify HNIG. A is wrong because MMR is a live vaccine and is contraindicated in pregnancy; it is also not the indicated PEP strategy here. B is tempting because of pregnancy and the narrow time window, but bypasses the required susceptibility assessment when prompt testing is available. C incorrectly applies the 72-hour preferred window as an absolute cut-off: HNIG may be used up to 6 days after exposure. D is wrong because one MMR dose does not allow presumed immunity in a pregnant woman born in 1990 or later.

Reference: UK Health Security Agency National measles guidelines, version 8 (July 2026) — https://assets.publishing.service.gov.uk/media/69cbc91fa60a12ca3913c644/ukhsa-national-measles-guidelines-version-7-march-2026.pdf Administration of HNIG for measles post-exposure prophylaxis (16 July 2026) — https://www.gov.uk/government/publications/immunoglobulin-when-to-use/administration-of-hnig-for-measles-post-exposure-prophylaxis