What is the recommended treatment for a pregnant woman diagnosed with toxoplasmosis?

Toxoplasmosis Diagnosis and Treatment in Pregnancy

Diagnostic Approach

Pregnant women with suspected acute toxoplasmosis must have confirmatory testing performed at a reference laboratory for toxoplasmosis, as false-positive IgM results from commercial laboratories are common and can lead to unnecessary treatment delays. 1

Initial Serologic Testing

• Baseline IgG testing should be performed at pregnancy diagnosis to identify women with chronic infection versus those susceptible to acute infection 2
• Positive IgM results from commercial laboratories require confirmation at a reference laboratory (such as Palo Alto Medical Foundation Toxoplasma Serology Laboratory) before initiating treatment 1
• The more sensitive IgM ISAGA test (available only at reference laboratories) should be used, as negative IgM ELISA at commercial laboratories cannot exclude congenital toxoplasmosis 1
• Repeat testing should be performed within 2-3 weeks if acute infection is suspected 3

Fetal Assessment

• Amniocentesis for PCR testing should be offered if maternal primary infection is confirmed, but not before 18 weeks gestation and at least 4 weeks after suspected maternal infection to avoid false-negative results 3
• Monthly fetal ultrasound monitoring should continue until delivery, looking for ventriculomegaly, hydrocephalus, intracranial calcifications, hepatosplenomegaly, or growth restriction 1, 3

Treatment Recommendations

For Maternal Infection Without Confirmed Fetal Infection (Before 18 Weeks)

Spiramycin 1 gram (3 million IU) orally three times daily should be initiated immediately upon suspicion of acute infection, even before confirmatory testing returns, and continued until delivery if fetal infection is not documented. 1

• Spiramycin is not teratogenic and is available in the United States only through the FDA Investigational New Drug process (telephone: 301-796-1600) 1
• Spiramycin concentrates in the placenta and may reduce maternal-fetal transmission by approximately 60% 4
• Early treatment initiation (within 3 weeks of seroconversion) can reduce transmission risk by 52% 5, 6

For Confirmed or Highly Suspected Fetal Infection (≥18 Weeks)

Switch from spiramycin to combination therapy with pyrimethamine, sulfadiazine, and folinic acid when fetal infection is confirmed by positive amniotic fluid PCR, abnormal fetal ultrasound findings, or maternal infection acquired at or after 18 weeks gestation. 1

• This combination therapy is recommended for three scenarios: (1) confirmed maternal infection at/after 18 weeks, (2) positive amniotic fluid PCR, or (3) abnormal fetal ultrasound suggestive of congenital toxoplasmosis 1
• Folinic acid (leucovorin) must be administered concurrently to prevent bone marrow suppression 7
• Pyrimethamine is Pregnancy Category C and has shown teratogenic effects in animal studies at doses 2.5 times the human therapeutic dose 7
• Semiweekly blood counts including platelet counts should be performed during high-dose therapy 7

Alternative Regimen

Recent evidence suggests that spiramycin combined with trimethoprim-sulfamethoxazole may be more effective than spiramycin alone (8.2% transmission rate vs. 20%) and appears non-inferior to pyrimethamine-sulfadiazine, though this requires prospective validation 8

Critical Timing Considerations

The timing of maternal infection profoundly affects both transmission risk and disease severity:

• First trimester (13 weeks): Transmission risk <15%, but when infection occurs, it causes the most severe disease including potential miscarriage 1, 5, 6
• Second trimester (26 weeks): Transmission risk increases to 44%, with moderate disease severity 1, 5
• Third trimester (37 weeks): Transmission risk reaches 71%, but disease severity is typically milder 1, 5

Special Populations

Immunocompromised or HIV-Positive Women

• These women require screening regardless of symptoms due to reactivation risk and potential for toxoplasmosis encephalitis 3
• Previously immune women who are severely immunocompromised during pregnancy can transmit infection through reactivation 1

Women with Chronic Infection

• Anti-toxoplasma treatment is not necessary in immunocompetent pregnant women with serologic evidence of chronic infection acquired before pregnancy (>3 months before conception) 1, 3
• Rare case reports exist of reinfection with different strains, but this is exceptional 1

Common Pitfalls to Avoid

• Do not rely on commercial laboratory IgM results alone - up to 50% of women with positive screening may be missed if only symptomatic or high-risk women are tested 1
• Do not perform amniocentesis before 18 weeks or within 4 weeks of suspected maternal infection 3
• Do not use spiramycin for documented fetal infection - it does not cross the placenta in therapeutic concentrations to treat the fetus 1, 4
• Never use pyrimethamine without folinic acid due to severe bone marrow suppression risk 7

Consultation Requirement

Consultation with medical experts familiar with toxoplasmosis management is strongly recommended for all cases of suspected or confirmed maternal infection during pregnancy. 1, 3