What are the dangers to the fetus from toxoplasmosis during pregnancy?

Dangers to the Fetus from Toxoplasmosis During Pregnancy

Congenital toxoplasmosis can cause severe neurological, ocular, and systemic damage to the fetus, with the risk and severity of complications inversely related to gestational age at maternal infection. 1

Risk of Transmission and Timing

• The overall risk of maternal-fetal transmission in women who acquire primary Toxoplasma infection during pregnancy is approximately 29% (95% CI: 25%-33%) 1
• Transmission risk varies significantly by trimester:
  • First trimester: 2-6% risk of transmission 1
  • Increases sharply throughout pregnancy, reaching up to 81% in the final weeks 1
  • Recent data shows symptomatic congenital toxoplasmosis rates of 15%, 44%, and 71% after maternal infections at 13,26, and 37 weeks of gestation, respectively 1
• While transmission risk increases with gestational age, the severity of fetal disease is typically worse when infection occurs earlier in pregnancy 1, 2

Specific Fetal and Neonatal Complications

Severe Manifestations

• Recent U.S. data from the National Reference Laboratory for Toxoplasmosis showed that 85% of infants with congenital toxoplasmosis were severely affected 1:
  • 92% had chorioretinitis 1
  • 80% had intracranial calcifications 1
  • 68% had hydrocephalus 1
  • 62% had all three of these manifestations 1

Neurological Complications

• Hydrocephalus and microcephaly 1, 3
• Intracranial calcifications 1, 3
• Seizures 4
• Mental retardation and neurocognitive impairment 5, 2

Ocular Disease

• Chorioretinitis leading to visual impairment or blindness 1, 2
• Even asymptomatic infants at birth are at high risk for developing ocular complications later in life 5

Systemic Manifestations

• Hepatosplenomegaly 1
• Jaundice 1
• Ascites 3
• Hematologic abnormalities including anemia, thrombocytopenia, and neutropenia 1
• Maculopapular rash 1
• Generalized lymphadenopathy 1

Delayed Manifestations

• 70-90% of congenitally infected infants are asymptomatic at birth 1
• However, up to 85% of initially asymptomatic infants will develop serious sequelae months or years after birth if untreated 5
• Late sequelae commonly include:
  • Progressive vision loss due to recurrent retinitis 2
  • Neurodevelopmental delays 2
  • Hearing impairment 5

Risk Factors for More Severe Disease

• Factors associated with increased risk of maternal-to-child transmission include 1:
  1. Acute primary T. gondii infection during pregnancy
  2. Maternal immunocompromising conditions
  3. Lack of antepartum treatment
  4. High T. gondii strain virulence
  5. High parasite load

Prevention and Treatment Considerations

• Prompt initiation of treatment within 3 weeks after maternal infection can reduce transmission odds by 52% compared to treatment started after 8 weeks 1
• For women with confirmed acute infection but no evidence of fetal infection, spiramycin is recommended for fetal prophylaxis 3
• If fetal infection is confirmed, a combination of pyrimethamine, sulfadiazine, and folinic acid is recommended 3, 5
• Treatment of infected pregnant women may modify disease severity even if fetal infection has already occurred 5

Important Caveats

• The incidence of congenital toxoplasmosis in the United States has decreased over time, from approximately 0.91 cases per 10,000 live births (1988-1999) to 0.23 cases per 10,000 live births (2006-2014) 1
• Diagnosis of maternal infection can be challenging and should be confirmed at reference laboratories before intervention 3
• Amniocentesis for diagnosis of fetal infection should not be performed before 18 weeks' gestation and should be done at least 4 weeks after suspected maternal infection 3