Serious complications of rubella are rare, particularly since the measles, mumps and rubella (MMR) vaccine was introduced.

In the small number of cases where an infection develops in pregnancy, however, there is a serious risk to the unborn baby.

If a pregnant woman catches rubella, the infection can be passed to her baby. This can result in problems such as miscarriage (the loss of the pregnancy during the first 23 weeks) and a range of birth defects known as congenital rubella syndrome (CRS).

Congenital rubella syndrome (CRS)

CRS occurs when the virus that causes rubella disrupts the development of an unborn baby. It is very rare in the UK nowadays, with only eight cases reported between 2002 and 2011.

The risk of CRS affecting the baby and the extent of the birth defects it causes depends on how early in the pregnancy the mother is infected. The earlier in the pregnancy, the greater the risk.

The risks are:

• infection in first 10 weeks – the risk of CRS is as high as 90% and the baby is likely to have multiple birth defects
• infection in 11th-16th weeks – the risk of CRS drops to around 10-20% and it is likely that affected babies will have fewer birth defects
• infection in 17th-20th weeks – CRS is very rare, with deafness the only problem reported

There is not thought to be any risk of CRS developing if you are infected with rubella after the 20th week of pregnancy.

If a pregnant woman does become infected with rubella during the first 20 weeks of pregnancy, there is no treatment that is known to be effective in preventing CRS.

Problems caused by CRS

CRS can cause the following problems in babies:

• cataracts (cloudy patches in the lens of the eye) and other eye defects
• deafness
• congenital heart disease (where the heart does not develop in the right way)
• a small head compared with the rest of the body, as the brain is not fully developed
• a slower than normal growth rate in the womb
• damage to the brain, liver, lungs or bone marrow

Children born with CRS can develop problems later in their lives as well. These include:

• type 1 diabetes – a long-term condition that is caused by too much glucose in the blood
• overactive thyroid or underactive thyroid – the thyroid gland produces hormones to control the body’s growth and metabolism 
• swelling inside the brain – this causes a loss of mental and movement functions

Occasionally, hearing problems are not obvious at birth, but are detected as the child gets older.