I am 24 weeks pregnant and I'm worried about chickenpox, as my three-year-old son has been exposed to it at his nursery. Is there any chance that the baby will be infected or damaged by chickenpox?

Dr Fred Kavalier answers your health question:

Chickenpox can cause problems to babies in the womb, but these problems are relatively uncommon. The first important question is whether you have had chickenpox yourself. If you have had chickenpox, then there is nothing to worry about, because you will be immune and this immunity will protect the baby in the womb.

If you are not sure whether or not you have had chickenpox, you should have a blood test to see if you are immune. You should know the results within a couple of days. If a pregnant woman who is not immune catches chickenpox during the first 20 weeks of pregnancy, there is a small risk (about two in 100) of the baby having fetal varicella syndrome. This can cause limb deformities, brain damage and damage to the eyes and skin of the baby.

Between 20 and 36 weeks of pregnancy, chickenpox in the mother will not harm the baby. Chickenpox in the last four weeks of pregnancy can infect the baby in the womb, and this can sometimes be severe and even life-threatening.

Please send your questions and suggestions to A Question of Health, 'The Independent', Independent House, 191 Marsh Wall, London E14 9RS; fax 020-7005 2182 or e-mail to health@independent.co.uk. Dr Kavalier regrets that he is unable to respond personally to questions.