Rubella in pregnancy is a viral infection that can cause miscarriage, stillbirth, or severe birth defects in the developing baby. The danger is highest during the first 12 weeks of pregnancy, when infection gives the baby up to a 90% chance of being born with a collection of serious problems known as congenital rubella syndrome (CRS). Thanks to widespread vaccination, rubella is rare in many countries today, but it still circulates globally, and anyone who isn’t immune remains at risk.
How Rubella Reaches the Baby
Rubella is a mild illness for most adults. It causes a low-grade fever, rash, and swollen lymph nodes that clear up within a few days. In pregnancy, though, the stakes change entirely. The virus can cross the placenta and infect the developing baby directly. During the first trimester, when organs are forming rapidly, this infection disrupts normal development in ways that often can’t be repaired.
The exact mechanism isn’t fully understood, but researchers believe the virus infects placental cells in early pregnancy, essentially opening a gateway to the fetus. Because the baby’s immune system is too immature to fight off the infection, the virus can persist in fetal tissues for months, interfering with cell growth during the most critical windows of organ formation.
Congenital Rubella Syndrome
CRS is the term for the pattern of birth defects that results when a baby is infected with rubella in the womb. It can affect nearly every organ system, and many of its consequences are lifelong.
The most common problems include:
- Hearing loss: the single most frequent outcome, often profound and permanent
- Heart defects: particularly problems with the blood vessel connecting the heart to the lungs, or narrowing of the pulmonary arteries
- Cataracts or glaucoma: clouding or pressure buildup in the eyes, sometimes present at birth
- Intellectual and developmental disabilities
- Low birth weight
Less common but still serious complications include brain damage, liver and spleen enlargement, jaundice, an abnormally small head (microcephaly), thyroid problems, and a characteristic blueberry-colored skin rash caused by bleeding under the skin. Some of these issues are apparent at birth. Others, like hearing loss or developmental delays, may not become obvious until months or years later.
Why the First Trimester Is Most Dangerous
Timing matters enormously. Infection in the first eight weeks of pregnancy carries the highest risk, with up to 90% of babies developing CRS. During this window, the eyes, heart, brain, and ears are all in early formation, and the virus can damage multiple systems simultaneously.
As pregnancy progresses, the risk drops significantly. Infection in the second trimester still poses some danger, particularly to hearing, but the likelihood and severity of birth defects decrease. By the third trimester, the baby’s organs are largely formed, and the risk of CRS is much lower, though not zero. This sharp drop-off is why early pregnancy is the period of greatest concern.
How Rubella Is Detected During Pregnancy
Most pregnant women are tested for rubella immunity through a routine blood test early in pregnancy. This test checks for a specific type of antibody (IgG) that indicates past infection or successful vaccination. In the United States, a level above 10 IU/ml is considered immune. If your results show immunity, rubella is not a concern for your pregnancy.
If you’re not immune and you’re exposed to someone with rubella, or if you develop symptoms like a rash and joint pain, your doctor will order blood tests looking for a different type of antibody (IgM) that signals a new, active infection. A rise in antibody levels between two blood draws taken a couple of weeks apart can also confirm recent infection.
Testing the Baby Before Birth
When a pregnant woman is confirmed to have a new rubella infection, particularly in the first trimester, testing the baby for infection becomes an option. This is done through amniocentesis, where a small amount of amniotic fluid is drawn and tested for the virus’s genetic material. The test is highly accurate, with close to 100% specificity and over 90% sensitivity when timed correctly.
Timing is important: amniocentesis should be performed at least six weeks after the suspected maternal infection, or after 20 weeks of pregnancy, whichever comes later. This waiting period ensures enough viral material is present in the fluid to be reliably detected. Ultrasound can also reveal signs of fetal infection, including restricted growth, an abnormally small head, brain calcifications, cataracts visible on imaging, and an enlarged placenta.
Treatment Options Are Limited
There is no antiviral medication that treats rubella, and no treatment can reverse damage already done to the developing baby. This is what makes rubella in pregnancy so different from many other infections: once the virus reaches the fetus during early organ development, the consequences are largely set in motion.
If fetal infection is confirmed in the first trimester, the conversation typically shifts to counseling about the expected outcomes and the range of disabilities the baby may face. The severity of CRS varies, some children have one or two affected organs while others have widespread damage, but there is no way to predict exactly how an individual baby will be affected based on testing alone.
Prevention Through Vaccination
The MMR (measles, mumps, rubella) vaccine is the single most effective protection against rubella in pregnancy, and it needs to happen before conception. The vaccine cannot be given during pregnancy because it contains a weakened live virus. If you receive the MMR vaccine, you should wait at least one month before becoming pregnant, and a blood test can confirm that your immunity has taken hold.
Ideally, rubella immunity is checked during a preconception visit or at a routine physical. If you’re already pregnant and your blood work shows you’re not immune, vaccination will need to wait. In that case, the priority is avoiding contact with anyone who has or may have rubella, especially if you’re traveling to regions where the virus still circulates widely.
Vaccination After Delivery
If you go through an entire pregnancy without rubella immunity, the standard recommendation is to receive the MMR vaccine soon after delivery. This protects you in any future pregnancy. The vaccine is safe for breastfeeding mothers. It does not affect the baby through breast milk, and breastfeeding does not interfere with how well the vaccine works.
Getting vaccinated postpartum closes the gap before another pregnancy. Since the recommended waiting period after vaccination is at least 28 days before conceiving, this timing works well for most families planning their next steps.
Why Rubella Still Matters
In countries with strong vaccination programs, rubella and CRS have become exceedingly rare. But “rare” is not “gone.” Outbreaks still occur in communities with low vaccination rates, and the virus remains common in parts of Africa, Southeast Asia, and the Eastern Mediterranean. A single unvaccinated traveler can reintroduce the virus to a population that has let its guard down.
For anyone planning a pregnancy, confirming rubella immunity is one of the simplest and most consequential steps in prenatal preparation. A single blood test and, if needed, a single vaccine can eliminate the risk entirely.