It depends. If you've had chickenpox before, you're probably immune. You're also likely to be immune if you received the chickenpox vaccine, which has been available in the United States since 1995.

A single dose of the chickenpox vaccine, which was the standard recommendation when it was first offered, effectively prevents the disease in 80 to 85% of people vaccinated and prevents a severe case in most others. Since then, research has shown that a second dose provides additional protection, so the Centers for Disease Control (CDC) now advises getting two doses of the chickenpox vaccine.

Because many adults are immune, very few pregnant women get chickenpox – estimates range from 1 to 5 cases for every 10,000 pregnancies. But you could get quite sick if you're not immune and do catch the disease while you're pregnant, and there's a chance that your baby would be affected. You can find out your immune status by having a simple blood test.

Chances are good that your baby would be fine. But if you get chickenpox during the first or second trimester, there's a slight risk (up to 2%) that your baby could get congenital varicella syndrome. The risk is highest if you're infected between weeks 13 and 20.

Congenital varicella syndrome is characterized by:

• Birth defects, most commonly skin scarring, malformed limbs, and an abnormally small head

• Neurologic problems (like intellectual disability)

• Physical disability

• Gastrointestinal complications

• Vision problems

• Low birth weight

• Seizures

• Increased risk of miscarriage or stillbirth

Having chickenpox during pregnancy could affect your health, too. It's already riskier for you to get the virus as an adult: Some adults who get the infection develop a condition called varicella pneumonia, which can be severe and even life-threatening. The risk of developing pneumonia may be higher if you're a smoker or if you get chickenpox during the third trimester. In pregnant women, this complication is also associated with higher rates of preterm birth.

If you come down with chickenpox, you'll have a detailed ultrasound to check for signs of defects or other problems and then have at least one follow-up ultrasound. You may also choose to meet with a genetic counselor or maternal-fetal medicine specialist to discuss your particular risks.

If you get chickenpox early in the third trimester, your baby will probably be fine. Here's why: About five days after you come down with chickenpox, your body produces antibodies to the virus, and these pass to your baby through the placenta. This gives them protection that their own immature immune system can't provide.

The most risky time to come down with chickenpox is between five days before giving birth and two days after delivery because during that time frame, your baby is exposed to the virus but doesn't have time to receive antibodies from you. In this case, there's a high risk (up to 50%) that they'll develop neonatal varicella, or newborn chickenpox, which can be a serious and even life-threatening condition, especially if left untreated.

Fortunately, your baby's risk of a severe case can be greatly reduced if they get a shot of varicella zoster immune globulin (VZIG), a blood product that contains chickenpox antibodies. (You may also see this referred to as VariZIG, which is the brand-name product available in the United States.) Your baby will be given the shot soon after birth if you develop chickenpox within five days of delivery, or as soon as you discover a rash if it's within two days after delivery.

The VZIG shot is also given to every baby born before 28 weeks (whether or not the baby could have the virus) and to all preterm babies born after 28 weeks whose mothers aren't immune.

Your newborn will get the antiviral drug acyclovir intravenously if they show any signs of the infection, such as a fever or a rash (even if it's just a few spots).

If you know you're immune, you don't need to do anything. If you're not sure, call your healthcare provider immediately to have a blood test. Chickenpox is highly contagious. If you're not immune and you have direct contact with an infected person, it's very likely that you'll get sick too. For example, if someone in your household has chickenpox and you're not immune, chances are 90% that you'll catch it.

If the blood test shows that you're not immune, you can get a shot of an antiviral medicine such as acyclovir or valacyclovir to reduce your chances of a severe infection and serious complications. It's best to get this shot within 24 hours of the rash appearing. The shot won't prevent fetal infection, but reduces the severity of your signs and symptoms.

It can take anywhere from 10 to 21 days after exposure, though most often you'll see signs after 14 to 16 days. At first, you may have mild flu-like symptoms, followed by an itchy rash. The rash starts out as little red bumps that blister as they get larger, then eventually dry out and scab over.

You'll probably see the rash first on your face, chest, or abdomen, and new eruptions will gradually appear on other parts of your body. You're contagious from about 48 hours before the first crop of bumps appears until they've all crusted over.

If you start to have symptoms and think you have chickenpox, call your healthcare provider right away. Don't show up unannounced at your provider's office because you could infect other pregnant women there. If you need to be seen, they'll make special arrangements so you won't sit in a crowded waiting room.

If you do have chickenpox, you might get a prescription for the antiviral drug acyclovir. Experts aren't sure yet if acyclovir reduces the risk for neonatal varicella syndrome, but it has been shown to help minimize fever and symptoms that you may experience (and also the duration of your symptoms), and it lowers the risk of complications from varicella pneumonia. If you develop any signs of pneumonia, like a fever with rapid breathing, discomfort when you breathe, or a cough, call your provider right away because your condition can get worse rapidly.

Call 911 if you have severe symptoms, such as trouble breathing or chest pain. All pregnant patients with suspected varicella pneumonia are usually hospitalized for treatment with IV acyclovir.

If you're not immune to chickenpox, take measures to avoid exposure:

• Avoid being around anyone who has or may have chickenpox. This includes anyone who's not immune and has come in contact with an infected person in the past three weeks, and anyone with flu-like symptoms. People with chickenpox are very contagious before they develop the telltale rash.

• Take care to avoid contact with anyone who you know has shingles, which is a condition that affects people who've already had chickenpox. (Most commonly it affects older adults and people with compromised immune systems.) With shingles, the chickenpox virus is reactivated, causing a painful, itchy skin rash. It's very rare for a pregnant woman to develop shingles, and, even if you did, the risk to your baby would be negligible. You can catch the chickenpox virus from someone with shingles, though.

• Make sure that all healthy children age 12 months or older and other susceptible members of your household are vaccinated, because you're most likely to catch chickenpox from someone who lives with you. This is especially important if they've recently been exposed to chickenpox, because getting vaccinated within a few days of exposure reduces their risk of coming down with the disease.

Although it's theoretically possible for a newly vaccinated person to transmit the chickenpox virus to someone else, the risk is minuscule. Only 13 cases have been confirmed since 1995, making it extremely rare. This is much lower than the chance of a susceptible family member contracting the virus and passing it to you during your pregnancy.

You can't get the chickenpox vaccine while you're pregnant. In fact, the CDC advises women to wait a month after getting the chickenpox vaccine before even trying to conceive.  If you do get the chickenpox vaccine before you know you're pregnant, talk to your doctor as soon as you learn of the pregnancy. Receiving the chickenpox vaccine within three months of pregnancy or in early pregnancy is still associated with a relatively low risk of congenital varicella syndrome.

Arrange to get the first dose of the vaccination right after you have your baby (and the second dose four to eight weeks later at your postpartum visit), so you don't have to worry about infection during a future pregnancy. It's safe to get the vaccine while you're breastfeeding.

Learn more:

Infections to watch out for during pregnancy

Is it safe to get vaccinated during pregnancy?