Pregnancy and Chickenpox

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Chickenpox is an infectious disease caused by a virus called varicella-zoster. It used to be a very common disease in school-aged children for a couple of reasons. The first reason was that chickenpox is extremely contagious, by way of sneezing or coughing, or direct contact. The second reason was that varicella-zoster was notorious for producing more serious disease in adults and teens, plus it was well-known that having the disease usually confers life-long immunity, although later a person can develop a disease called shingles. Knowing this, during school outbreaks of the virus, it was common in the mid 20th century for parents to expose uninfected siblings of infected children on purpose in order to finish with the virus for the entire household. Sometimes, there would be “chickenpox parties.” However, this practice has subsided since the mid 1990s when a vaccine for varicella-zoster was licensed in the US and its use started to spread. The parties were never a good idea, since it’s possible, even for young children, to develop severe complications from chickenpox.

Ironically, the availability of the vaccine for the past two decades means that chickenpox today is just as much an adult condition as a childhood condition. This is because young adults who have never been vaccinated also are likely never to have been exposed to the virus during childhood; thus, if they do happen to be exposed to the virus later, they will develop a fairly severe case of chickenpox. This includes women who were children and teens in the late 1990s and early 2000s. Such women are becoming pregnant today. If you are planning a pregnancy and have not received the varicella vaccine, and have never had chickenpox, it is recommended that you get vaccinated prior to pregnancy.

The spread of chickenpox through populations has changed dramatically since the introduction of the varicella-zoster vaccine. About four million cases used to develop yearly in the United States and the disease used to account for 11,000 hospitalizations per year. Because of the available vaccine, the number of cases has dropped by 90 percent since the mid 1990s. Therefore, today there are roughly 400,000 cases in the US each year and the number continues to drop. These days, such cases are limited to those who have problems with their immune system and those who have not been vaccinated. However, if you are not vaccinated against varicella-zoster, you are at just as much risk of developing chickenpox as someone who is not pregnant.

When chickenpox does develop, the classic symptoms are fever, coughing, loss of appetite, headache, and most notoriously a very itchy rash consisting of red or reddish pox marks throughout the body. If you are already pregnant when you develop chickenpox, you should not receive the vaccine at that at point, because it is a live vaccine. However, you do not need to terminate your pregnancy, as there are ways to treat you.

Chickenpox is a clinical diagnosis, meaning that it is diagnosed based on the symptoms that you develop, based on a history of being exposed to the virus without having immunity, and based on timing of the appearance of the symptoms. The typical pattern is that you develop itch pox marks on the torso and scalp first and then the rash spreads to the face and arms and legs. Fever, headache, and loss of appetite all develop in course, and usually the rash starts 10-21 days after you are exposed to another person who turns out to have chickenpox. If you develop such symptoms, if you had contact with somebody who developed chickenpox recently, if you have never had chickenpox, and if you have never been vaccinated against chickenpox, the diagnosis of chickenpox is almost certain.

Usually, chickenpox is a mild disease, but itching all over the body together with a fever can make you feel miserable, particularly while you are pregnant. Furthermore, a fraction of cases of chickenpox can develop complications. These include bacterial infections from scratching pox, which in some cases can spread from the skin into the body and lead to blood infection (septicemia), lung infection, and infection of bones or joints. The varicella-zoster virus itself can cause infections too, leading to pneumonia and even infection of the brain.

Any fever that develops with chickenpox can be harmful to the fetus or embryo, if you do not treat the fever immediately with fever-lowering medication, such as acetaminophen or paracetamol. Additionally, the varicella-zoster virus may harm the child directly, depending on when in the pregnancy you become infected. If you are infected with varicella-zoster during the first 20 weeks of pregnancy, and especially from gestational week 8 to gestational week 20, there is a small but real chance (0.4 – 2 percent) that it can lead to what is called congenital varicella syndrome (CVS). CVS is a collection of very severe congenital defects that include underdeveloped legs and arms, a brain that is small and underdeveloped, and eye and skin problems. On the other hand, if you happen to develop chickenpox during the last few days before delivery, your baby could be born with neonatal varicella, which can be fatal.

If you develop chickenpox while pregnant, your doctor may offer you an antiviral drug called acyclovir, or a similar drug that works the same way. If you have been exposed to varicella-zoster virus within the past 10 days, but have not yet developed chickenpox, you will be offered an injection of what doctors call immune globulin, which contains antibodies that help protect against the virus. Both treatments are less risky for the fetus or embryo than being inside a mother who has full-blown chickenpox. Acetaminophen and paracetamol, given for fever, also are considered to be safe during pregnancy. Acyclovir, acetaminophen, and paracetamol are considered safe during breastfeeding. Alongside medications, oatmeal baths have a use in chickenpox in alleviating the itching.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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