Chickenpox in Pregnancy

Why chickenpox in pregnancy is treated so seriously

UKHSA states the reason plainly: "Chickenpox (varicella) infection in immunosuppressed individuals, susceptible pregnant individuals and neonates can result in severe and even life-threatening varicella disease."

RCOG's guideline on chickenpox in pregnancy adds the fetal side: varicella in pregnancy "may cause maternal mortality or serious morbidity. It may also cause fetal varicella syndrome (FVS) and varicella infection of the newborn, which includes congenital varicella syndrome (CVS) and neonatal varicella."

UKHSA sets out what the risks look like by stage: "Chickenpox infection during the first 20 weeks of pregnancy can lead to fetal varicella syndrome, which includes microcephaly, cataracts, growth retardation limb hypoplasia, and skin scarring. Chickenpox can cause severe maternal disease and this risk is greatest in the second or early in the third trimester."

The change most sources have not caught up with

For decades the answer to chickenpox exposure in pregnancy was varicella-zoster immunoglobulin, VZIG. That is no longer the UK approach for pregnant contacts, and any page still telling you to expect an immunoglobulin injection is out of date.

UKHSA's current guidance states: "Oral aciclovir (or valaciclovir) is now the first choice of PEP for susceptible immunosuppressed individuals, all susceptible pregnant women at any stage of pregnancy and infants at high risk."

The change originated in a national VZIG shortage in 2018 that prompted an expert review, and the evidence gathered afterwards supported antivirals as the standard rather than as a substitute. Antivirals are named here as treatments; doses are set by your clinician and are not published on this page.

The timing rule that sounds wrong but is not

Most post-exposure treatment is given immediately. This one is not. UKHSA: "Antivirals (oral aciclovir or valaciclovir) should be given from day 7 to day 14 after the first day of exposure."

The exposure day is defined precisely: "The day of exposure is defined as the date of onset of rash if the index is a household contact and date of first or only contact if the exposure is on multiple or single occasions respectively."

If you present late, there is still a window: "If the patient presents after day 7 of first exposure, a 7-day course of antivirals can be started up to day 14 after first exposure." And repeat exposures matter — a second exposure within the first 7 days of treatment may mean the course is extended, and an exposure 8 or more days after the first means a new course.

The practical point is that you must make contact quickly even though treatment starts later. The assessment, the antibody test and the prescription all have to happen inside that window.

Whether you need anything at all

Post-exposure prophylaxis is only for people who are not already immune. UKHSA sets three criteria that must all be met: "significant exposure to chickenpox (varicella) or shingles (zoster) during the infectious period"; being "at increased risk of severe chickenpox such as immunosuppressed individuals, neonates and susceptible pregnant women"; and "no antibodies to varicella-zoster virus (VZV) — urgent VZV antibody testing can be performed within 24 hours".

For pregnant women, history is often enough: "For immunocompetent individuals including pregnant individuals, a history of previous chickenpox, shingles or 2 doses of varicella vaccine is sufficient evidence of immunity."

Where there is no such history, blood is tested, and there is a specific threshold: "Where testing is undertaken, antiviral PEP is recommended if VZV IgG is less than 100 milli-international units per millilitre (mIU/ml)." Your booking bloods can often be used — UKHSA notes "booking blood samples are acceptable for pregnant women if available", which can save days.

The risk if nothing is done is not small. UKHSA cites that "in the absence of PEP, the risk of developing varicella in susceptible contacts is high with 13 of 18 (72%) of seronegative pregnant women developing varicella following a significant exposure".

Is aciclovir safe in pregnancy?

UKHSA addresses this directly: "Although oral aciclovir and valaciclovir (prodrug of aciclovir) are not licensed in pregnancy, there is extensive evidence of safety in pregnancy, including from 2 large registries of infants whose mothers were exposed to aciclovir in pregnancy." It adds that from follow-up across 24 countries between 1984 and 1999 of over 1,200 pregnancies exposed to oral or intravenous aciclovir at all stages, no unusual pattern of defects was seen.

It also notes that "aciclovir is also recommended for treatment of chickenpox in pregnant women who have reached 20 weeks or more gestation" — so antivirals appear both as prophylaxis after exposure and as treatment if you actually develop chickenpox.

If you develop the rash

Contact your maternity team or GP straight away rather than attending in person without warning — the NHS advises people with chickenpox not to go near "newborn babies or anyone who's pregnant or has a weakened immune system", and the same applies to you in a waiting room full of pregnant women.

Seek urgent advice for breathlessness, chest pain, a cough, a dense or bleeding rash, drowsiness or confusion. Varicella pneumonia is the complication that makes chickenpox dangerous to adults, and pregnancy increases that risk.

Timing near birth matters most of all. Where a mother develops chickenpox in the period around delivery, the baby needs specific protection, and UKHSA has a separate pathway for neonates whose mothers develop chickenpox in the 7 days before to 7 days after delivery. If you develop a rash near your due date, say so immediately.

Shingles, and the difference

Shingles in someone else can transmit varicella to a susceptible person through contact with the fluid in the blisters, which is why UKHSA's guidance covers exposure to "chickenpox (varicella) or shingles (zoster)". It is less infectious than chickenpox and requires closer contact, but exposure to shingles in a non-immune pregnant woman still counts as an exposure worth reporting.