Rubella, commonly known as German measles, is a viral infection that is generally mild in children and adults. Routine screening for rubella immunity is a standard part of prenatal care worldwide due to the potential risks during pregnancy. The specific test used is the Rubella Immunoglobulin G (IgG) antibody assay. This test is designed to measure the presence of long-term protective antibodies, which are generated either from a past rubella infection or from receiving the Measles, Mumps, and Rubella (MMR) vaccine. The results of this IgG test help determine if the pregnant individual has adequate protection against the virus.
Why Rubella Screening is Essential During Pregnancy
The primary purpose of rubella screening during pregnancy is to identify individuals who are susceptible to the infection. If a non-immune person contracts the rubella virus while pregnant, the infection can pass from the mother to the developing fetus, potentially causing severe harm. This condition is known as Congenital Rubella Syndrome (CRS), which can result in a range of serious developmental issues.
The risk of severe fetal damage is highest when the mother is infected early in the pregnancy. If the infection occurs within the first 12 weeks of gestation, the risk of the baby being affected by CRS can be as high as 85% to 90%. CRS can lead to multiple birth defects, including congenital cataracts, deafness, intellectual disabilities, and heart defects like patent ductus arteriosus.
The risk to the fetus decreases significantly after the first trimester, but infection up to 16 weeks still carries a substantial risk of malformation. Identifying non-immune individuals through the IgG test allows healthcare providers to implement precautions to avoid exposure throughout the pregnancy. This proactive approach is essential for preventing the devastating outcomes associated with maternal rubella infection.
Interpreting Rubella IgG Test Results
The Rubella IgG test measures the concentration of “memory” antibodies in the blood, which serve as an indicator of immunity. Understanding the three possible test results—positive, negative, and equivocal—is necessary for proper management. The specific numerical cutoffs for these categories may vary slightly between laboratories, but the general interpretation remains consistent.
A Positive (Reactive) result, often defined by an IgG level above a specific threshold such as 10 or 15 International Units per milliliter (IU/mL), indicates immunity. This means the individual has sufficient antibodies to protect both themselves and the fetus from rubella infection. No further action or vaccination is required.
A Negative (Non-Reactive) result means the IgG antibody level is below the established threshold for immunity, suggesting the individual is susceptible to the virus. A negative result requires careful attention and planning to prevent infection and protect the current and future pregnancies.
An Equivocal (Indeterminate) result is one that falls within a narrow range close to the immunity cutoff. This result is inconclusive and suggests that the level of protective antibodies is too low to definitively confirm immunity. Healthcare providers usually recommend repeating the IgG test after a short period or conducting further evaluation, such as an IgM test, to clarify the immune status.
Navigating Non-Immunity and Vaccination Planning
Non-immunity, confirmed by a negative Rubella IgG result, requires a clear plan to protect the mother and baby. Since the MMR vaccine contains a live-attenuated virus, it cannot be administered during pregnancy due to the theoretical risk to the fetus. The primary focus during gestation is strict avoidance of exposure to the virus.
Non-immune pregnant individuals should take precautions to minimize contact with anyone who may have a rash illness, which could be rubella. If an exposure is suspected, the healthcare provider must be notified immediately for further testing, which would include both IgG and IgM antibodies, to check for a recent infection.
Vaccination immediately following birth protects future pregnancies. The MMR vaccine is typically administered before the non-immune mother is discharged from the hospital or shortly thereafter. This post-delivery timing ensures the mother is protected before any subsequent conception, as women are generally advised to avoid becoming pregnant for about 28 days following the vaccination.
The administration of the MMR vaccine postpartum is considered safe for breastfeeding mothers. Although the rubella vaccine virus may be secreted into breast milk, it is attenuated and has not been shown to cause illness in the infant. Vaccination is encouraged to provide the mother with the necessary immunity and prevent the possibility of CRS in future children.