Rubella IgG and IgM - Diagnosis of Rubella in Pregnancy

Rubella is a viral infection that usually causes mild frames, with few or no symptoms in most patients. It is a benign disease in the vast majority of cases, being less dangerous than the flu, for example.


Rubella, however, has a special feature that makes it a major public health concern: it is extremely dangerous to the fetus when acquired by mother during pregnancy, especially in the first 3 months of pregnancy. For this reason, serology for rubella, test used to diagnose this virus, should always be part of the exams performed during prenatal care.

In this article we will stick to the interpretation of serology rubella during pregnancy. We will explain what the terms IgG or IgM reagent, non-reactive and indeterminate, and what are the implications for the mother and the fetus in each type of result.

One of the most common ways to diagnose an infection is by serology, which is a blood test in which we can search for the existence or not of specific antibodies against certain diseases.

The logic behind the serology is: when we are infected by a germ, be it a fungus, bacterium, parasite or virus, our immune system "catch" samples of these microbes and uses them to create specific antibodies against them. If you've never been exposed to a particular microbe before, you do not have specific antibodies against it. On the other hand, if you have the disease now, or had at some point in life, we managed to find specific antibodies circulating in the bloodstream.

Since antibody production takes several days to be completed, those patients who are having a first infection must initially using immune other weapons, which antibodies to attack the invading agent. One example is the white blood cells, also called leukocytes, which are immune cells that can attack any type of infectious agent. In many cases, the disease can be mild enough to be controlled with non-specific defense cells, before the antibodies are ready.

Some diseases, however, can only be completely eliminated when the first specific antibodies arise. Importantly, each group antibody is specific to a particular disease. Their antibodies against toxoplasmosis not serve to combat rubella, as well as antibodies against chickenpox no use against measles.

I will use rubella as an example, but the reasoning will develop from now used for most infections.

IgM and IgG antibodies

When we are infected with a new infection, first produced antibodies are immunoglobulins M, commonly known as IgM. Therefore, the existence in the blood of large amounts of IgM antibodies against rubella, for example, is an indication that infection has recently been acquired. So a serology IgM positive result for rubella indicates ongoing infection.

When the patient is cured of the infection, the immune system to produce IgM antibodies and starts to produce immunoglobulin G, known as IgG. The IgG antibody is a memory that remains in the blood for life. In this way, the next time the patient contact rubella, the risk of developing the disease will be minimal, because from the first moment, your immune system will already have specific antibodies against rubella samples.

Therefore, the presence of IgG antibody against rubella is a sign that the patient has had the disease at some point in life and now is immunized. The presence of IgG antibodies is often called a serological scar, or a mark that the patient was infected in the past.

IgG antibodies can be obtained by previous infection or vaccination. Indeed, the goal of any vaccination is to induce the immune system to produce permanent antibody against a particular infection. The development of IgG antibodies is an indication that the vaccination has been effective.

When the patient makes a serology rubella, there are basically three possible outcomes:

• 1. IgM and IgG non-reactive.
• 2. IgM reactive and IgG non-reactive.
• 3. IgM non-reactive and IgG reactive.

1. What does the result: IgM and IgG non-reactive?

If in your serology rubella both IgM and the IgG come as no reagents, it means you do not have antibodies against rubella, or has never been exposed (a) to this virus and is susceptible to an infection. If you have been vaccinated (a), but its IgG is non-reactive, it means that vaccination was not effective, which is an indication to repeat the vaccine.

A pregnant woman who has negative serology for rubella need to be very careful not to come into contact with anyone infected, because, as she has no antibodies against rubella, it runs the risk of contamination during pregnancy.

2. What does the result: IgM reactive and IgG non-reactive?

As mentioned above, the IgM antibody appears after a few days of infection with rubella. As rubella virus takes about 2 to 3 weeks to manifest symptoms, in most cases, the IgM antibody reagent is longer when the patient begins to manifest disease. After 4 to 8 weeks, the production of IgM serology greatly decreases and becomes not the reagent.

Therefore, a pregnant with positive serology for IgM means she probably infected with the rubella virus in the last 2-6 weeks, being at risk of having a fetus with malformations, especially if the pregnancy is in the first quarter.

3. What does the result: IgM non-reactive and IgG reactive?

The presence of a reagent for rubella IgG is known to cause some confusion in pregnant women. Contrary to what most think of the lay population, this result is still well present in early pregnancy, it is best that the pregnant woman can have. Consider this: if the mother has a reagent IgG, it only indicates that she has an immune scar, or is immune to rubella. This immunity may have been obtained by an ancient infection before she became pregnant, or by prior vaccination. The fact is that the origin of IgG not matter, the important thing is that this pregnant have a very low risk of contracting rubella during her pregnancy because she has antibodies against the virus.

It is necessary, however, an observation. The IgG antibody indicates past infection, usually over two months, but he does not allow us to say exactly when the infection occurred. Therefore, serology must be done at the first prenatal consultation to be interpreted correctly. Imagine a pregnant woman only makes serology in the 5th or 6th month of pregnancy and has a positive IgG. If she has not had symptoms, we have no way of knowing whether the infection occurred years ago or emerged in the first weeks of pregnancy.

The reference values for serology rubella may vary from one laboratory to another. When interpreting the result, not the value itself the most important, but whether he is or not reagent reagent according to the reference values provided by the laboratory.

I picked up randomly on the Internet the reference values of a particular lab only to exemplify.

Reference values for the IgG rubella:

• No reactive: less than 5 IU / mL
• Undetermined: 5-15 IU / mL
• Reactive: greater than 15 IU / mL

Reference values for rubella IgM:

• No reactive: less than 0.6 IU / mL
• Undetermined: 0.6 to 0.79 IU / mL
• Reactive: greater than 0.79 IU / mL

In the above example, any patient with IgG lower than 5 IU / ml IgM or less than 0.6 IU / ml did not have a positive result, ie negative. Likewise, if IgG is greater than 15 IU / ml IgM or greater than 0.79 IU / ml, will result reagent.

What is an indeterminate result?

Indeterminate or inconclusive result occurs when IgM or IgG amount is slightly changed, it is not possible to say whether there are any relevant quantities of antibodies or not. Generally, this problem occurs when some unidentified factor is interfering in the result. When this occurs, the ideal is to repeat the exam. In most cases, when the patient with an indeterminate result repeats serology, the new result comes as no-reagent.

In the first prenatal visit, all pregnant women should do serology rubella so that their doctors are aware of their immune status against the disease. The initial examination is to know who is immunized and who is susceptible to disease.

Serology for rubella should also be asked if during pregnancy, pregnant women have contact with any infected person or develop typical symptoms of rubella, such as fever, enlarged lymph nodes and patches throughout the body. The diagnosis of rubella serology is done to detect the presence of IgM reagent. Another way is to make a diagnosis by comparing the IgG values at the time of symptoms and after 3 weeks. Even if the remaining IgM negative, the IgG levels rise more than 4 times during this interval, this indicates that the symptoms have even caused by rubella.

A person having more than once rubella is not common, but it is not impossible. Similarly, it is not impossible that a person who has been vaccinated develop rubella. So if a pregnant woman in the first prenatal examination had positive IgG develop a clinical picture similar to rubella, the possibility of re-infection by the rubella should be considered. In these cases, the suggested approach is the following:

• If pregnancy is less than 12 weeks, a new serological test should be performed. A significant rise in IgG levels compared to the first survey strongly suggests the hypothesis of re-infection by rubella. Fortunately, the risk of malformations in reinfection is only 8%, much lower than the 80% risk in primary infection.
• If the pregnancy has already exceeded 12 weeks, no need to do anything, since the risk of malformations in this phase is very low in cases of reinfection.

A simple measure to immunize pregnant women who did not have IgG reagent, or which are likely to rubella during pregnancy would be vaccination during pregnancy. Unfortunately, current vaccines against rubella are made with live attenuated virus, which contraindicate its use during pregnancy.

So the best way to prevent rubella in pregnancy is through mass vaccination of girls during childhood. If you have been vaccinated in accordance with the vaccination schedule, the risk of rubella in a future pregnancy becomes much lower.

As the risk of major malformations is extremely high in the first quarter, many countries, such as Portugal, permit abortion when pregnant have the misfortune of contracting rubella exactly the first weeks of pregnancy. In Brazil, however, abortion is not permitted in this situation. In these cases, there is nothing to do, just hope that the infection does not cause serious damage to the baby.

Rubella acquired after the 20th of pregnancy rarely causes malformations, but may cause some problems, such as premature birth or babies with low birth weight.