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Pregnancy and chickenpox don’t mix

Concerned pregnant female holding belly

If a pregnant woman catches chickenpox (varicella), her fetus is at risk for a rare complication known as congenital varicella syndrome. The syndrome affects perhaps 1% to 2% of babies born to mothers who develop chickenpox before the 20th week of pregnancy; in absolute numbers, that means perhaps 4 babies per year in Canada and 41 in the United States. It is also very serious: nearly 30% of babies with the syndrome die within a few months after birth, while others may have severe birth defects such as leg deformities, eye diseases, and neurological problems.

Chickenpox is highly contagious, and can be transmitted even with brief contact. After exposure, treatment with an antibody called varicella-zoster immune globulin (VZIG) can reduce the levels of chickenpox virus in a woman’s blood or prevent her from developing chickenpox altogether; this in turn can potentially prevent congenital varicella syndrome. German and British clinical practice guidelines recommend this precaution in women who have no immunity to chickenpox, but North American guidelines do not. Because of this, doctors may not always think of suggesting VZIG to pregnant women who are at risk.

A review published in CMAJ, the journal of the Canadian Medical Association, observes that there are no randomized controlled trials of VZIG for prevention of congenital varicella syndrome, and this use is “off-label.” However, the review authors point out, this does not mean there is no evidence for its use. The authors analyzed data from 3 prospective cohort studies that followed a total of 640 pregnant women who were diagnosed with chickenpox. Of those, 142 were treated with VZIG; among this group, no babies were born with congenital varicella syndrome. Among the remaining 498 women who were not treated with VZIG, 14 babies (2.81%) were diagnosed with congenital varicella syndrome.

The authors and an accompanying commentary recommend the use of VZIG in women who have been exposed to chickenpox, and strongly urge that the North American guidelines be revised.

Preventing congenital varicella syndrome

  • If you are planning a pregnancy and have never had chickenpox, or you are not sure you have had it, talk to your doctor about chickenpox vaccination. This is the best way to avoid chickenpox in pregnancy.
  • If you are pregnant and have been exposed to chickenpox or shingles, see your doctor right away. Exposure includes being in the same room as someone with chickenpox or shingles for 15 minutes, or at least 5 minutes of face-to-face contact.
  • Varicella-zoster immune globulin (VZIG) can prevent chickenpox or reduce the amount of virus in the blood if it is given within 96 hours after exposure.


 For more information

Cohen A, Maschopoulos P, Stiehm RE, Koren G. Congenital varicella syndrome: the evidence for secondary prevention with varicella-zoster immune globulin. CMAJ 2011; available online at

Sauerbrei A. Preventing congenital varicella syndrome with immunization. CMAJ 2011; available online at