Infectious Diseases

Measles and Pregnancy: Risks by Trimester, Critical Weeks, and What to Do After Exposure

Measles infection during pregnancy can increase risks of miscarriage, preterm birth, and severe maternal illness. Learn trimester-specific risks and how to reduce harm.

Updated: 4 min read

Measles and Pregnancy

Intro

Measles (rubeola) is a highly contagious viral infection that can cause more severe illness during pregnancy. While measles does not typically cause a well-defined congenital syndrome, infection — especially in early pregnancy — is associated with miscarriage, preterm birth, and serious maternal complications.

Because the MMR vaccine is usually not given during pregnancy, prevention relies on pre-pregnancy immunity and urgent action after exposure.

For general disease information, see Measles (Rubeola).

Key Points

  • Measles infection during pregnancy can lead to pregnancy loss and preterm delivery
  • First trimester infection carries the highest miscarriage risk
  • Severe maternal illness (pneumonia, hospitalization) is more common in pregnancy
  • Measles does not cause a classic congenital malformation syndrome
  • Prevention before pregnancy is the safest strategy

Pregnancy Risk Stratification

High risk:

  • Unvaccinated or no proof of immunity
  • Exposure during outbreak
  • First trimester infection

Medium risk:

  • One documented MMR dose

Low risk:

  • Two documented MMR doses / proven immunity

Why Measles Is Riskier During Pregnancy

Pregnancy alters immune and respiratory function. When measles occurs, this can result in:

  • Higher viral burden
  • More severe fever and inflammation
  • Increased risk of pneumonia and hospitalization
  • Greater physiological stress on the placenta and fetus

Risks by Trimester

First Trimester (Weeks 1–12) — Highest Risk Period

The first trimester, especially weeks 5–10, is the most vulnerable period.

Associated risks include:

  • Miscarriage / spontaneous abortion
  • Severe maternal fever contributing to fetal loss
  • Dehydration and systemic illness affecting placental support

Measles does not reliably cause structural birth defects, but early pregnancy loss risk is clearly elevated.

Second Trimester (Weeks 13–27)

Risks shift from miscarriage to pregnancy complications, including:

  • Preterm labor
  • Placental dysfunction
  • Maternal pneumonia requiring hospitalization

Fetal growth restriction has been reported in some cases, likely secondary to maternal illness rather than direct viral effects.

Third Trimester (Weeks 28–Birth)

Later pregnancy infection is associated with:

  • Preterm birth
  • Increased likelihood of cesarean delivery due to maternal illness
  • Risk of neonatal measles if infection occurs near delivery

Maternal respiratory compromise is a major concern in this stage.

Maternal Complications

Pregnant people with measles have higher rates of:

  • Pneumonia
  • Hospital admission
  • Dehydration and electrolyte imbalance
  • Rare but serious neurological complications

Before Pregnancy: Best Protection

If pregnancy is planned or possible:

  • Confirm two documented MMR doses
  • If records are unclear, discuss serologic testing or vaccination
  • If MMR is given, follow local guidance on the recommended waiting period before conception

During Pregnancy: Reducing Exposure Risk

During outbreaks:

  • Avoid crowded indoor environments where feasible
  • Minimize time in waiting rooms
  • Ensure household contacts are vaccinated if eligible
  • Follow public health guidance closely

What to Do After Possible Exposure

  1. Contact your clinician or public health unit immediately
  2. Provide:
    • Gestational age
    • Vaccination history or uncertainty
    • Time and location of exposure
  3. Follow guidance on:
    • Post-exposure management
    • Symptom monitoring
    • Isolation if symptoms develop

FAQ

Q: What if my immunity is unclear during pregnancy? A: Discuss serologic testing with your clinician. If confirmed non-immune, focus on minimizing exposure risk and knowing your action plan after exposure.

Q: Can I be around people recently vaccinated with MMR? A: Yes. MMR vaccine virus is generally not spread from vaccinated individuals to others.

Q: Does measles infection guarantee problems for the baby? A: Not all pregnancies with measles result in adverse outcomes, but the risks are elevated compared to uninfected pregnancies. The highest risks occur with infection in early pregnancy.

Educational only; not a substitute for professional medical advice.