How should a pregnant woman at ≥28 weeks gestation be managed after rubella exposure?

Management of Rubella Exposure in Third Trimester

For a pregnant woman at ≥28 weeks gestation exposed to rubella, obtain immediate serologic testing if immune status is unknown, closely monitor for symptoms, but do NOT administer immune globulin as it does not prevent infection or congenital rubella syndrome—then ensure MMR vaccination immediately postpartum before hospital discharge. 1

Immediate Assessment and Testing

• Determine immune status immediately by checking rubella IgG antibody levels if not already documented in prenatal records 1
• A negative rubella IgG test indicates susceptibility and requires heightened surveillance 1
• Only IgG levels ≥10 IU/mL are considered clearly protective; equivocal results (5-9.99 IU/mL) should be treated as susceptible 1
• Obtain detailed exposure history including timing, duration, and proximity of contact 1

Critical Management Decision: NO Immune Globulin

Immune globulin (IG) is NOT recommended for post-exposure prophylaxis because it will not prevent infection or viremia, and may only modify or suppress symptoms, creating a false sense of security 1. This is a common pitfall—IG has not been proven effective in preventing congenital rubella syndrome 1.

Surveillance Protocol

• Monitor closely for rubella symptoms including rash, fever, and lymphadenopathy over the next 2-3 weeks 1
• If symptoms develop, obtain serum for rubella-specific IgM antibody testing between 1-2 weeks after rash onset for optimal detection 1, 2
• For asymptomatic exposure, obtain acute-phase serum as soon as possible after exposure, with convalescent-phase serum drawn ≥28 days after exposure 3, 2
• Paired sera testing should demonstrate a fourfold rise in IgG titer to confirm infection 2

Reassurance About Third Trimester Risk

• At ≥28 weeks gestation, the risk of congenital rubella syndrome is significantly lower than in the first trimester 1
• The risk of congenital defects is up to 85% when infection occurs in the first 8 weeks, declining to 10-24% at 13-16 weeks, and is rare after 16 weeks 1, 4, 5
• Defects are rarely noted when fetal infection occurs after the 16th week of gestation 4

Maternal Complications to Monitor

• Monitor for rare maternal complications including thrombocytopenia (1 per 3,000 cases) and encephalitis (1 per 6,000 cases), which are more common in adults 1
• Joint symptoms (arthralgia/arthritis) occur in up to 70% of infected adult women and typically resolve spontaneously within 1 day to 3 weeks 1, 2

Mandatory Postpartum Intervention

Administer MMR vaccine before hospital discharge after delivery if the woman is seronegative or has equivocal immunity 1. This is the single most critical intervention to prevent congenital rubella syndrome in future pregnancies:

• Postpartum vaccination of all women not known to be immune could prevent approximately 40% of congenital rubella syndrome cases 1
• Vaccination must occur before discharge because follow-up vaccination programs have proven less successful than immediate postpartum administration 1
• Counsel the patient to avoid pregnancy for 3 months following vaccination 1
• Breastfeeding is NOT a contraindication to vaccination, even though virus may be excreted in breast milk 1

Common Pitfalls to Avoid

• Do not delay vaccination until a postpartum clinic visit—voluntary vaccination programs have been less successful than mandatory programs 1
• Do not rely on clinical diagnosis alone—clinical diagnosis of rubella is unreliable, and only laboratory confirmation is reliable evidence of infection 1, 4
• Do not routinely recommend pregnancy termination based solely on confirmed maternal infection at this gestational age—adequate prenatal counseling and diagnostic workup are mandatory 1
• Approximately 10-20% of women of childbearing age remain susceptible to rubella despite childhood vaccination programs, making postpartum vaccination crucial 1, 4, 6