For most people, chicken pox is an annoying but medically harmless childhood illness that conjures memories of itchy red spots and kids slathered in pink Calamine lotion. But for a pregnant woman who is not immune to chicken pox, the illness poses a potential threat to her fetus. The good news is that this is an extremely uncommon problem, and a treatable one if it does occur.
What Is Chicken Pox? Am I At Risk?
Chicken pox is caused by varicella zoster virus, a member of the herpesvirus family.1 The infection is passed from person to person through respiratory droplets or close contact. The disease, also known as varicella, usually causes fever, fatigue, and a distinctive rash that starts out as flat, small, red dots and turns into small, itchy blisters. Once you get chicken pox, you have immunity for life, unless your immune system becomes impaired, such as after a bone marrow transplant or during cancer chemotherapy.
After having chicken pox, the virus doesn’t leave your body, but instead, travels to your spinal cord and stays there forever. The virus can get activated later in life and reappear as shingles (also known as herpes zoster): a rash of red, painful blisters in a small part of your body. When this happens, the disease is contagious only by direct contact with the fluid from the blisters, so if they are covered, the illness is not transmitted from person to person.
Most adults are immune to chicken pox because they either had it as children or received the vaccine. The vaccine became available in the US in 1995, and was widely adopted soon thereafter. Although most cases are benign, before the vaccine about 150 people died every year from chicken pox. Because of the success of the vaccine, there are few cases of natural chicken pox in the US now, and very few deaths.
Currently, most women of childbearing age had the actual disease. But some may still be at risk. If you have no history of chicken pox and have not had the vaccine, you may be at risk. Some people have no memory of having had chicken pox, but are still immune, because they had an extremely mild case of chicken pox. But if you are unsure, be sure to talk to your obstetrician about this. A simple blood test can determine if you are immune to chicken pox.
What Are The Effects Of Chicken Pox On My Baby And Me?
First of all, be aware that chicken pox in pregnant women is very uncommon. Before chicken pox vaccination was routine, infection in pregnant women occurred at a rate of only 0.4-0.7 per 1,000 pregnant women. And now that the disease is even less common due to the vaccination, this rate is most likely even less.1
When pregnant women get chicken pox, the virus can cross the placenta and cause serious problems in the fetus. When this occurs, it is called congenital varicella syndrome,1-4 that consists of:
- distinctive scarring of the skin
- damage to the eyes, including chorioretinitis, cataracts, and atrophy of the optic discs
- limb hypoplasia: poor growth of arms and legs
- microcephaly: small head
- intrauterine growth retardation
- developmental delay and learning problems
Up to 30% of infants with congenital varicella syndrome will die in the first few months of life.3
Fortunately, congenital varicella syndrome is extremely rare. As noted above, having chicken pox during pregnancy is uncommon. And the risk of having an infant with congenital varicella syndrome is about 4 out of every 10,000 infected pregnancies.1,5 The highest risk for the fetus occurs during weeks 13 to 28 of pregnancy. The risk of the fetus getting congenital varicella syndrome after week 28 is practically zero.3
For the woman, chicken pox during pregnancy can result in pneumonia in 10-20% of cases.1,3 If the mother gets varicella in the time period from 5 days before delivery to 2 days after delivery, then the infant is at high risk of getting chicken pox.1,3
How Is Chicken Pox Treated In A Pregnant Woman?
As with many infections, the first step is prevention. If you are not currently pregnant, get vaccinated. If you are pregnant or trying to conceive, then hold off on the vaccination. The vaccine contains the live varicella virus, and there is a theoretical risk that the vaccine could cause congenital varicella syndrome. However, in the first 17 years after the vaccine was introduced in the U.S., no adverse effects were found in any pregnant women who inadvertently received the vaccine.3,6 Even so, the vaccine is currently contraindicated in pregnant women.
If a pregnant woman does contract chicken pox, the treatment consists of giving an oral medicine, acyclovir, which will decrease the severity and duration of the illness. In severe cases of chicken pox, intravenous (IV) acyclovir may be given. Acyclovir, either oral or IV, will help the mother’s chicken pox, but will not prevent congenital varicella syndrome.1,4,7,8
For pregnant women who are not immune but have been exposed to chicken pox, they should be given an IV preparation of varicella zoster immunoglobulin (VZIG). This is known as passive immunization, because it involves giving antibodies to varicella, which will protect the mother for a brief period of time, but not forever. This should also prevent congenital varicella syndrome in the fetus. The VZIG is effective if given within the first 10 days after exposure.1,3,4,7,8
What Can I Do To Avoid Chicken Pox?
First, remember that most women of childbearing age currently are already immune to chicken pox because of prior infection or vaccination. And if you are immune and pregnant, then being exposed to someone with chicken pox will not harm you or your baby.
But if you are unsure about your immunity, ask your doctor. A simple blood test can determine if you are immune or not. If you are not immune, be sure to do the following:1,3,4,7,8
- If you are not currently pregnant, get vaccinated. This is the best way to prevent infection during pregnancy
- Avoid contact with anyone who has chicken pox
- Avoid close contact (touching) with anyone with shingles
- Tell your doctor if you have contact with anyone who has chicken pox or shingles
- Tell your doctor if you have any signs of chicken pox: fever, rash, fatigue
- Make sure you get the vaccination after delivery of your baby
1 American Congress of Obstetricians & Gynecologists. Practice bulletin no. 151: Cytomegalovirus, parvovirus B19, varicella zoster, and toxoplasmosis in pregnancy. Obstet Gynecol. 2015 Jun;125 (6):1510-25.
2 Ahn KH, Park YJ, Hong SC, et al. Congenital varicella syndrome: A systematic review. J Obstet Gynaecol. 2016 Jul;36 (5):563-6.
3 Gnann JW, Jr. Varicella-zoster virus: Prevention through vaccination. Clin Obstet Gynecol. 2012 Jun;55 (2):560-70.
4 Bialas KM, Swamy GK, Permar SR. Perinatal cytomegalovirus and varicella zoster virus infections: epidemiology, prevention, and treatment. Clin Perinatol. 2015 Mar;42 (1):61-75, viii.
5 Harger JH, Ernest JM, Thurnau GR, et al. Frequency of congenital varicella syndrome in a prospective cohort of 347 pregnant women. Obstet Gynecol. 2002 Aug;100 (2):260-5.
6 Marin M, Willis ED, Marko A, et al. Closure of varicella-zoster virus-containing vaccines pregnancy registry – United States, 2013.
7 Kovacs G BP. Infections During Pregnancy–Varicella, Herpes, Cytomegalovirus, Toxoplasma, Listeria, Group B Streptococcus. In: Lectures in Obstetrics, Gynaecology and Women’s Health. Switzerland: Springer, Cham; 2015:133-7.
8 Shrim A, Koren G, Yudin MH, Farine D, Maternal Fetal Medicine C. Management of varicella infection (chickenpox) in pregnancy.