Pregnant women who have not had chickenpox should be advised to avoid contact with people with the virus and be referred to a specialist if they develop the rash, say updated guidelines from the Royal College of Obstetricians and Gynaecologists (RCOG).

The advice, published on Wednesday, says women should be asked about previous chickenpox or shingles infections when they book in for antenatal care and told to quickly inform healthcare workers of a potential exposure to either illness.

Many women have antibodies to protect themselves against the virus after contracting the illness as a child but estimates suggest chickenpox, which usually causes a mild infection in children, complicates three in every 1,000 pregnancies.

Prof Patricia Crowley, from University College Dublin, and co-author of the guideline, the fourth edition to be published, said: “Chickenpox is rare in pregnancy and many adults will have had the virus when they were younger and are therefore immune.

“However, chickenpox can be serious for your health during pregnancy and complications can arise.

“It is vital that pregnant women with symptoms of the virus should contact their GP as soon as possible and avoid contact with potentially susceptible individuals, such as other pregnant women and babies.”

After contacting their doctor, women who develop chickenpox in pregnancy should be referred to a foetal medicine specialist and a neonatologist should be informed of the birth, the guidelines say.

Dr Manish Gupta, co-chair of the RCOG guidelines committee, said: “Women may worry about passing the virus on to their baby.

“However, this is quite rare and depends on what stage of pregnancy the virus was transmitted.”

The advice says that ideally there should be a minimum of seven days between onset of the rash and delivery of the baby but emphasises that timing and delivery should be individualised for each women.

Women with chickenpox should breastfeed if they wish to and are well enough to do so, it says.

Louise Silverton, director for midwifery at the Royal College of Midwives, welcomed the new guidance.

She added: “Pregnancy can be very confusing for women as they are taking in a huge amount of information and we need to ensure that women know what to look for without causing overload.

“Midwives will need to discuss this with all women, particularly new migrants who may be unaware if the have had it and may have limited language and understanding.”