Chickenpox in Pregnancy
Background
Varicella zoster virus (VZV) causes chickenpox (primary infection) and shingles (reactivation). Around 90% of UK adults are seropositive, so primary infection in pregnancy is uncommon (~3/1000 pregnancies) but carries maternal, fetal, and neonatal risks. Maternal complications include varicella pneumonitis, hepatitis, and encephalitis, which are more severe in pregnancy, particularly the third trimester and in smokers.
Assessing Exposure and Post-Exposure Prophylaxis
- A "significant exposure" is face-to-face contact or being in the same room for ≥15 minutes with a person with chickenpox or exposed shingles.
- Any pregnant woman with a reliable history of chickenpox, or two documented doses of varicella vaccine, can be reassured — no testing or PEP is needed.
- If history is uncertain, check VZV IgG urgently; a quantitative result <100 mIU/mL is considered non-immune/susceptible.
- Current first-line PEP (UKHSA, all trimesters): oral aciclovir 800 mg four times a day, started on days 7–14 after exposure (not immediately) — this has superseded VZIG as first-line prophylaxis. Oral valaciclovir 1000 mg three times a day is an acceptable alternative.
- VZIG is now reserved only for women who cannot tolerate oral antivirals (e.g. malabsorption, renal toxicity).
- A further exposure after a completed antiviral course warrants a fresh risk assessment and, if indicated, a repeat course starting 7 days after the new exposure.
Management of Established Chickenpox in Pregnancy
- Refer to a specialist for assessment of maternal complications (pneumonitis, encephalitis) and fetal risk.
- Oral aciclovir should be offered if the woman presents within 24 hours of rash onset and is ≥20+0 weeks gestation. Aciclovir is not licensed in pregnancy but is used on a risk–benefit basis with the woman's consent.
- Below 20 weeks, aciclovir may still be considered case by case rather than routinely offered.
- VZIG has no therapeutic benefit once a rash has developed and must not be given after chickenpox is established.
- IV aciclovir is used for severe disease (pneumonitis, encephalitis) or in the immunocompromised, especially around the time of birth.
- Where clinically appropriate, delivery should be deferred for 5–7 days after maternal rash onset to allow passive antibody transfer to the fetus.
Fetal Risk: Congenital Varicella Syndrome (FVS)
- Maternal infection before 28 weeks carries an overall FVS risk of around 1%; risk is highest (~2%) for infection between 13 and 20 weeks and very low before 13 weeks. FVS after 28 weeks is exceptionally rare.
- Features: dermatomal skin scarring, limb hypoplasia, microcephaly, cortical atrophy, chorioretinitis/cataracts, and other neurological damage.
- Detailed ultrasound (with referral to fetal medicine) is offered 5 weeks after infection to look for FVS features; amniocentesis for VZV PCR is not routinely recommended given the low predictive value.
- Maternal shingles is not associated with a significant FVS risk because of pre-existing maternal antibody.
Neonatal Varicella
- The highest-risk window is maternal rash onset from 5 days before to 2 days after delivery — the neonate is born before protective maternal IgG has transferred.
- Untreated neonatal varicella in this window has historically carried mortality as high as 20–30%; VZIG and aciclovir, plus intensive supportive care, have reduced this substantially.
- Affected neonates should receive VZIG as soon as possible after birth and be monitored closely (with aciclovir if signs of infection develop), and isolated from susceptible contacts.
- If maternal rash appears more than 7 days before delivery, the neonate is usually protected by transplacental antibody and disease, if it occurs, tends to be mild.
High-Yield Exam Points
- UKHSA PEP guidance has changed practice: oral aciclovir (days 7–14 post-exposure) is now first-line, not VZIG.
- VZIG is only for women who cannot take oral antivirals, and is never given once a rash has appeared.
- Aciclovir treatment of established chickenpox: offer if within 24h of rash AND ≥20 weeks.
- FVS risk: ~1% overall <28 weeks, peak ~2% at 13–20 weeks, negligible >28 weeks.
- Highest neonatal risk window: maternal rash 5 days before to 2 days after delivery.
- Shingles in pregnancy does not cause FVS.
Source: RCOG Green-top Guideline No. 13 (Archived — post-exposure management is now driven by UKHSA's *Guidelines on post-exposure prophylaxis (PEP) for varicella or shingles* (Jan 2023, updated Oct 2024) and UKHSA's Aug 2024 guidance on investigating viral rash exposure in pregnancy; GTG13 received a minor 2024 update to incorporate the UKHSA PEP recommendations, and its content on treatment, fetal, and neonatal risk below remains clinically relevant and exam-relevant) (21 January 2015 (4th edition); minor update 2024 to align with UKHSA PEP guidance)
Read the original on rcog.org.uk
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