Risk of Miscarriage with Fever in First Two Weeks of Pregnancy
While specific data on miscarriage risk from fever in the first two weeks of pregnancy is limited, evidence from Q fever infections and general fever studies suggests an increased risk, with first trimester infections carrying the highest miscarriage risk compared to later gestational ages.
Evidence from Specific Infections
The most direct evidence comes from Q fever studies, where:
- Women with Q fever during pregnancy face an 81% adverse fetal outcome rate when untreated, which drops to 40% with appropriate antibiotic treatment 1
- First trimester Q fever infection specifically carries the highest risk for miscarriage compared to second or third trimester infections 1, 2
- Second and third trimester infections are more likely to cause premature delivery rather than miscarriage 1, 2
The CDC explicitly states that women infected with Q fever during pregnancy are at increased risk for miscarriage and preterm delivery 3.
General Fever Data
From broader fever studies in pregnancy:
- High fever (≥38.9°C) lasting ≥24 hours in early pregnancy is associated with increased stillbirth rates (2.6% vs 0% in controls) 4
- Neural tube defects occurred in 5.9% (2/34) of women with high fever during the critical period for neural tube closure, compared to 0% in controls 4
- A systematic review found between 1.5- to nearly 3-fold increased risk of neural tube defects, congenital heart defects, and oral clefts with first trimester fever exposure 5
Critical Timing Considerations
The first two weeks of pregnancy represents the earliest embryonic period when the conceptus is most vulnerable:
- First trimester infections demonstrate the highest risk for both miscarriage and progression to chronic maternal disease 1, 2
- The pattern suggests earlier exposure carries greater miscarriage risk, while later exposure shifts toward preterm delivery and growth restriction 1
Protective Factors
Important mitigating information:
- Antipyretic medications (acetaminophen) may have a protective effect when used during febrile episodes 5
- Acetaminophen is the only safe first-line antipyretic during pregnancy and may provide protective effects against fever-related fetal harm 1, 2
Clinical Implications
Any pregnant person with fever in early pregnancy should receive immediate acetaminophen treatment 1, 2. If livestock exposure exists or fever is unexplained, empiric trimethoprim-sulfamethoxazole with folic acid supplementation should be initiated immediately without waiting for serologic confirmation 1, 2, as this reduces adverse outcomes from 81% to 40% 1.
Key Caveats
- Most available data comes from symptomatic infections requiring medical attention, not mild self-limited fevers 6, 4
- The exact quantification of miscarriage risk specifically in weeks 1-2 of pregnancy remains poorly defined in the literature, as most studies group "first trimester" together 5, 4
- It remains unclear whether the fever itself or the underlying infection causes the harm 3