Rubella in pregnancy is an infection caused by the rubella virus that can cross the placenta and cause serious birth defects, miscarriage, or stillbirth. The risk is highest in early pregnancy: up to 85% of babies develop congenital defects when infection occurs in the first 12 weeks. Thanks to widespread vaccination, rubella is rare in many countries, but it remains a real threat for unvaccinated women and in regions without routine immunization programs.
How Rubella Affects a Pregnant Woman
Rubella is often a mild illness in adults. After an average incubation period of 17 days, it typically produces a faint rash that starts on the face, spreads across the body within 24 hours, and fades within about three days. Swollen lymph nodes, particularly behind the ears and at the base of the skull, often appear before the rash and last five to eight days. A low-grade fever is common. Notably, 20% to 50% of infected people never develop a rash at all, which means a pregnant woman can be infected without obvious signs.
Joint pain or swelling occurs in up to 70% of adult women with rubella, making it one of the more noticeable symptoms. A woman is contagious from seven days before the rash appears to seven days after, so she can unknowingly spread the virus before she feels sick. This window of silent contagion is part of what makes rubella dangerous in pregnancy: exposure can happen before anyone realizes there’s a risk.
How the Virus Reaches the Baby
The placenta normally acts as a barrier between a mother’s blood and her baby’s. Rubella gets around this by infecting specific cells in the placenta called trophoblasts. Once the virus reaches certain placental cells positioned near maternal blood vessels, it can work its way into the core of the placenta and eventually into fetal blood vessels. Studies of placentas from rubella-affected pregnancies show inflammation, reduced placental weight, and damage to the tiny blood vessel structures (villi) that exchange nutrients and oxygen.
Inside the fetus, the virus slows cell growth and kills developing cells. This is especially destructive early in pregnancy, when organs are forming rapidly. The earlier the infection, the more organ systems are still in critical stages of development, which is why first-trimester infection causes the most widespread damage.
Risk by Trimester
The timing of infection dramatically changes the odds of harm to the baby. Maternal rubella during the first 12 weeks of pregnancy causes congenital defects in up to 85% of newborns. Between weeks 13 and 16, the rate drops to about 50%. During the second half of the second trimester, it falls to roughly 25%. Infection in the third trimester carries the lowest risk of structural birth defects, though it can still cause problems.
Beyond birth defects, rubella in early pregnancy increases the risk of miscarriage and stillbirth. Some pregnancies end before the effects on the baby are ever identified.
Congenital Rubella Syndrome
When the virus damages a developing baby, the resulting condition is called congenital rubella syndrome, or CRS. The classic pattern involves three problems: sensorineural hearing loss (the most common single defect), cataracts, and heart defects. These three together are sometimes called the Gregg triad, after the Australian ophthalmologist who first linked rubella to birth defects in 1941.
CRS can also cause intellectual disability, an abnormally small head (microcephaly), and calcifications in the brain, particularly around the base and brainstem. Some babies appear healthy at birth but develop hearing loss or learning difficulties in the months and years that follow. The severity depends on when during pregnancy the infection occurred and how extensively the virus disrupted organ development.
Globally, an estimated 32,000 cases of CRS occurred in 2019. About 75% of those cases were concentrated in just 19 lower- and middle-income countries that had not yet introduced rubella vaccination into their routine immunization schedules.
Testing and Immunity
Rubella immunity is checked with a simple blood test that measures a specific type of antibody called IgG. A level above 10 IU/mL is considered protective in the United States. If you were vaccinated as a child or had rubella in the past, you likely have lifelong IgG antibodies. This test is commonly included in early prenatal bloodwork.
If a pregnant woman is exposed to rubella and her immunity status is unknown, doctors test for two types of antibodies. IgG antibodies indicate past immunity, while IgM antibodies signal a recent or active infection. IgM typically becomes detectable four to 30 days after the rash appears. An additional test called IgG avidity can help distinguish a brand-new infection from one that happened months or years ago. Low avidity IgG suggests infection within the past four months; high avidity points to older immunity from a previous infection or vaccination.
For babies born to mothers who had rubella during pregnancy, IgM antibodies can be detected in the newborn’s blood for up to six months after birth, confirming congenital infection.
What Happens After Exposure During Pregnancy
If you’re pregnant and exposed to someone with rubella, the first step is determining whether you’re already immune. If prior blood tests show protective IgG levels, the risk to your baby is extremely low. If no immunity is documented, blood testing for both IgG and IgM antibodies will clarify whether you’re protected, susceptible, or already infected.
For women found to be susceptible, the main strategy is avoiding further exposure. That means staying away from settings where rubella might be circulating for six weeks after the last known case. There is no antiviral treatment for rubella, and no reliable way to prevent the virus from reaching the baby once a mother is infected. Immunoglobulin (a concentrated dose of antibodies given by injection) is sometimes offered within 72 hours of exposure, but it does not reliably prevent infection or protect the fetus. It may reduce symptoms in the mother.
The rubella vaccine cannot be given during pregnancy because it contains a live, weakened virus. Women who are found to lack immunity during pregnancy are vaccinated immediately after delivery, including if they’re breastfeeding. The vaccine is safe for nursing mothers.
Vaccination Before and After Pregnancy
Rubella vaccination is the single most effective way to prevent CRS. The vaccine is given as part of the MMR (measles, mumps, rubella) shot, which most people receive in childhood. If you’re planning a pregnancy and unsure of your immunity, a blood test can check. If you need the vaccine, the CDC recommends waiting at least one month after vaccination before becoming pregnant.
If prenatal blood tests reveal you’re not immune, you’ll be offered the MMR vaccine right after giving birth. This protects future pregnancies. By 2023, 175 of 194 countries had added rubella-containing vaccines to their routine childhood immunization programs, up from 99 countries in 2000. In countries with established vaccination programs, rubella and CRS have become extremely rare. The United States eliminated rubella transmission in 2004, though imported cases still occasionally occur.
For women who received childhood vaccination but show borderline or low antibody levels during pregnancy, a booster after delivery can strengthen immunity for future pregnancies.