Finding the right tests…
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Finding the right tests…
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Rubella IgG is a blood test that checks whether you're immune to rubella, a viral infection that's usually mild in children and adults but can cause miscarriage or serious birth defects if a pregnant woman catches it. IgG antibodies appear weeks after infection or vaccination and then stay in your blood for life, so a positive result here means your immune system already knows how to fight the virus - it does not mean you're currently infected. This test is used most often before or early in pregnancy, to confirm immunity exists before a woman is ever exposed to the actual virus.
The result is reported as reactive (immune) or non-reactive (not immune), sometimes alongside a numeric antibody level. A reactive IgG result means you have lasting immunity, whether from a past infection or from the MMR vaccine - the test cannot tell which. A non-reactive result means you have no documented protection against rubella, which matters most if you are, or are planning to become, pregnant, since vaccination isn't given during pregnancy itself and needs to happen before or after.
IgG antibodies take a few weeks to build up after either a rubella infection or the MMR vaccine, but once established they typically last a lifetime. A reactive rubella IgG result confirms that protection exists - it doesn't distinguish childhood infection from vaccination, and for practical purposes, that distinction doesn't matter.
Rubella is usually mild on its own, but it's one of the more dangerous infections a developing baby can be exposed to, especially in the first trimester, when it can cause miscarriage or congenital rubella syndrome. Checking IgG status before conception, or very early in pregnancy, tells a doctor whether a woman is protected before any exposure risk arises.
- If you're not pregnant, the MMR vaccine is given, and immunity is usually rechecked afterward - If you are already pregnant and non-reactive, the vaccine cannot be given until after delivery, since it uses a live virus - A non-reactive result in pregnancy means avoiding anyone with a rubella-like illness becomes more important until delivery
This test looks for long-term immunity, not a current infection. If a recent infection is suspected, doctors add an IgM test, since IgG can't distinguish a brand-new infection from old immunity by itself.
No, a positive IgG result means you have long-term immunity, from a past infection or from vaccination, not a current infection. If a recent infection is actually suspected, your doctor adds an IgM test instead.
It means you don't have documented protection against rubella. The vaccine can't be given during pregnancy since it uses a live virus, so your doctor may recommend avoiding contact with anyone with a rubella-like illness and vaccinating after delivery.
No, IgG antibodies look the same either way, and the test can't distinguish the two sources. For practical purposes, both provide the same lasting protection.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Labs typically report the result as reactive or non-reactive, sometimes with a numeric antibody index alongside it. Ranges and cutoffs vary by lab, so check what your own report states as the threshold for immunity.
There's no fasting requirement for this test. Ask your doctor or the centre when you book, particularly if it's being done alongside other antenatal blood work.
Checking before you start trying to conceive gives enough time to vaccinate and build immunity if you're found to be non-reactive, since the vaccine isn't given during pregnancy. Ask your doctor for the right timing for your situation.