Rubella immunity in pregnancy

6 December 2013

Dr Louise Newson explains how to test women for rubella immunity and when to vaccinate.

Risk of fetal damage from infection declines to 10-20% at 11-16 weeks

Rubella is usually a mild, self-limiting viral infection, but it can have severe consequences if it is contracted during pregnancy.

This is now a very uncommon infection in the UK as a result of the vaccination programme; there were 42 documented cases in the UK in 2012 and there have been two documented cases so far in 2013.¹

However, rubella is still common in many developing countries and worldwide, more than 100,000 children every year are born with congenital rubella syndrome (CRS).

Rubella in pregnancy

Maternal rubella infection during pregnancy may result in fetal loss or CRS.

CRS is the major complication of maternal infection in early pregnancy. This is an entirely preventable disease.

It can lead to deafness, cataracts, glaucoma, congenital heart disease, progressive encephalopathy and mental retardation.

Inflammatory lesions can occur in the brain, liver, lungs and bone marrow.

Infection in the first eight to 10 weeks of pregnancy results in damage in up to 90% of surviving infants. The risk of damage declines to about 10-20% with infection occurring between 11 and 16 weeks.

Fetal damage is rare with infection after 16 weeks of pregnancy.

TESTING FOR RUBELLA IMMUNITY
Current recommendations regarding testing for immunity A sensitive immunoassay for rubella-specific IgG should be used, capable of providing quantitative results in IU/mL. Qualitative or semiquantitative assays based on latex agglutination should not be used. A result <10IU/mL indicates rubella susceptibility. However, no report with a screening test result <10IU/mL should be issued until a confirmatory test has been performed, ideally by an alternative analytical method. Laboratories should verify that the assay used is sufficiently sensitive and precise, to ensure accurate results.

TESTING FOR RUBELLA IMMUNITY

Current recommendations regarding testing for immunity

A sensitive immunoassay for rubella-specific IgG should be used, capable of providing quantitative results in IU/mL.

Qualitative or semiquantitative assays based on latex agglutination should not be used.

A result <10IU/mL indicates rubella susceptibility. However, no report with a screening test result <10IU/mL should be issued until a confirmatory test has been performed, ideally by an alternative analytical method.

Laboratories should verify that the assay used is sufficiently sensitive and precise, to ensure accurate results.

Testing for immunity

The UK National Screening Committee advises that all pregnant women should be screened for rubella immunity by testing for rubella antibodies (IgG).²

As testing in this way is not actually beneficial for the woman's current pregnancy, it is recommended that all women of childbearing age should be opportunistically screened for rubella infection, in case they do not have immunity from their childhood vaccination.

Women who are found not to be immune to rubella and are not pregnant should be given the MMR vaccine before any future pregnancies.

They should avoid becoming pregnant until at least 28 days after the MMR vaccination.

Specimens with antibody levels ≥10IU/mL are reported as 'rubella antibody detected'. Specimens with antibody levels <10IU/mL are reported as 'rubella susceptible - two doses of MMR vaccination recommended post-delivery'.

If a woman has already received two or more documented doses of rubella vaccine and then has detectable levels of rubella antibody, but <10IU/mL, further doses of vaccine are unlikely to be of benefit. These women should be advised to seek medical advice if exposed to a rash illness during pregnancy.³

In recent years, the number of pregnant women susceptible to rubella has markedly increased. In the West Midlands, the proportion was shown to have risen from 1.4% in 2004 to 6.9% in 2011.⁴

It is thought that the number of non-immune women will continue to rise as a consequence of low MMR uptake in the late 1990s.

Some pregnant women need medical advice if exposed to a rash illness

Exposure to rubella

It is important to ensure that pregnant women exposed to rubella without adequate proof of immunity are evaluated for rubella-specific IgM and IgG antibodies.

Susceptible pregnant women should be counselled regarding the risks for intrauterine rubella infection and it is recommended that they restrict contact with persons with confirmed, probable, or suspected rubella for at least six weeks after the onset of the rash.³

If a pregnant woman thinks she has been exposed to rubella, she needs to seek medical advice. If she has had one of the following, she should be reassured the likelihood of rubella is remote and specific rubella investigation is not required, but to return if a rash develops:

At least two documented doses of rubella vaccine.

One documented dose of vaccine followed by at least one previous rubella antibody screening test which has detected rubella antibody ≥10IU/mL.

At least two previous rubella antibody screening tests which have detected antibody, in at least one of which, rubella antibody is ≥10IU/mL.

However, if the woman does not fulfil one of the above criteria, serum should be obtained as soon after contact as possible and tested for IgM and IgG, with a second sample four weeks later similarly tested if the patient is shown to be susceptible.

Any evidence of seroconversion or IgM positivity should be referred for confirmatory testing.

MMR vaccination

In the UK, MMR is given in the second year of life and again as a preschool booster. This vaccine has been proven to be safe, immunogenic and effective.⁵

Two doses of MMR are required to produce satisfactory protection against measles, mumps and rubella.

MMR vaccine can be given irrespective of a history of measles, mumps or rubella infection.

Breastfeeding is not a contraindication to MMR immunisation, and MMR vaccine can be given to breastfeeding mothers with no risk to their baby. There is no evidence of mumps and measles vaccine viruses being found in breast milk.⁶

There is also no evidence that rubella-containing vaccines are teratogenic.

Termination of pregnancy following inadvertent immunisation is not recommended. The woman and her partner should be given information on the evidence of lack of risk from vaccination in pregnancy.

Surveillance of inadvertent MMR administration in pregnancy is being conducted by the Health Protection Agency (HPA) immunisation department, to whom such cases should be reported (see Resources).

Where rubella protection is required for postpartum women who have received anti-D immunoglobulin, no deferral is necessary because response to the rubella component is normally adequate.

Blood transfusion around the time of delivery may inhibit the rubella response, so a test for rubella antibody should be undertaken six to eight weeks after vaccination. The vaccination should be repeated if necessary.