Chickenpox in pregnancy

What is chickenpox?

Chickenpox is an infection with a virus known as varicella zoster. A primary infection with chickenpox (that is, the first time you've had the infection) can cause serious illness and even death in a pregnant woman, and either a condition known as congenital varicella syndrome or varicella infection (chickenpox) in the baby.

Having shingles (a recurrence of the virus which has been dormant in the body) while pregnant doesn't seem to have any serious consequences for the unborn baby.

Symptoms of chickenpox

• Mild fever
• Itchy rash of red spots, which crust over and resolve after about 12 days

Causes and risk factors of chickenpox

Chickenpox, which is highly contagious, is spread by respiratory droplets and close personal contact. The incubation period is ten to 20 days and the person developing chickenpox becomes infectious from about 48 hours before the typical rash appears.

In theory a person continues to be infectious until the last of the blister-like spots (which ooze large amounts of the virus) crust over, although transmission of the infection has never been reported after the fifth day of the rash.

More than 90 per cent of pregnant women show antibodies to varicella-zoster virus, which means they've had the infection in childhood, sometimes without realising it. In this case they may be resistant to further infection. However, it's now thought that immunity to chickenpox can wane in a significant number of people and that reinfection may occur more commonly than was once thought. So even if a woman had chickenpox as a child, she may get it again (although second infections are often more mild). And a woman who hasn’t had chickenpox before is more vulnerable to it.

As a general rule, the first infection with chickenpox is a more serious illness in adults than in children. For example, about three in every 1,000 pregnant women develop chickenpox. About 10 per cent of these then get pneumonia. The complications from chickenpox in pregnancy very rarely may be fatal.

If chickenpox occurs early in the pregnancy there's a small risk of congenital varicella syndrome, which includes eye problems, underdeveloped limbs and brain damage. This develops in about two per cent of women who get chickenpox before 20 weeks of pregnancy and one per cent before 13 weeks.

Infection after 20 weeks of pregnancy doesn't seem to cause congenital varicella syndrome but may give the baby chickenpox while still in the womb, which can lead to severe symptoms in the first few days of life. This is most likely if the mother has chickenpox close to delivery.

Treatment of chickenpox

If you think you might have caught chickenpox then urgent treatment is important. Doctors may first do a blood test to check whether you already have your own antibodies to chickenpox. If not, injections of immunoglobulin (antibodies) to varicella may be offered to try to prevent infection developing. These should be given as soon as possible after contact, ideally within 96 hours.

If you, or your baby, develop chickenpox and become ill, then antiviral drugs such as acyclovir may be used to try to reduce the extent of the rash and other symptoms. (There's a vaccine against chickenpox but it isn't recommended once you're pregnant, because of a potential risk to the foetus.)