Treatment of Influenza at 18 Weeks Gestation
Start oseltamivir 75 mg orally twice daily for 5 days immediately, without waiting for laboratory confirmation of influenza. 1, 2, 3, 4
Immediate Treatment Protocol
Oseltamivir is the first-line antiviral agent for pregnant women with suspected or confirmed influenza at any gestational age, including 18 weeks. 1, 2, 4
- Dosing: 75 mg orally twice daily for 5 days 1, 2, 3
- Timing: Initiate treatment immediately upon suspicion of influenza, ideally within 48 hours of symptom onset, but do not withhold treatment if this window has passed 1, 4
- No testing required: Do not delay treatment while awaiting diagnostic test results—empiric treatment based on clinical suspicion is appropriate 1, 4
- Take with food: This significantly reduces the most common side effects of nausea and vomiting 1
Alternative Treatment Option
Zanamivir 10 mg (two 5 mg inhalations) twice daily for 5 days can be used if oseltamivir is contraindicated or unavailable. 1, 2
- However, zanamivir should be used with caution in pregnant women with underlying respiratory conditions such as asthma due to potential for bronchospasm 5, 6
- Oseltamivir remains the preferred first-line agent 1
Safety Profile in Pregnancy
Oseltamivir is safe throughout pregnancy, including the first and second trimesters. 1, 2
- No adverse effects have been reported among women who received oseltamivir during pregnancy or among infants born to such women 1
- The FDA classifies oseltamivir as Pregnancy Category C, but extensive post-marketing surveillance and observational data demonstrate reassuring safety outcomes 1
- A 5-year retrospective cohort of over 10,000 women found no association between first trimester influenza vaccination and major congenital malformations 1, 2
- Only 1% of patients discontinue treatment due to gastrointestinal side effects 1
Clinical Rationale for Aggressive Treatment
Pregnant women at 18 weeks gestation face significantly elevated risks from influenza infection that justify immediate antiviral treatment. 1, 2, 7
- Pregnant women are at higher risk for severe illness, pneumonia, ICU admission, and death compared to non-pregnant women 1, 2
- The relative risk for hospitalization increases from 1.4 during weeks 14-20 of gestation (which includes 18 weeks) to 4.7 during weeks 37-42 1, 2
- Influenza infection during pregnancy is associated with increased odds of congenital anomalies, stillbirth, late pregnancy loss, preterm delivery, low birth weight, and small-for-gestational-age infants 1, 2, 7
- Fever itself poses risks to fetal development, so treating influenza with oseltamivir may actually reduce fetal risk by shortening illness duration and reducing fever 1
Warning Signs Requiring Urgent Evaluation
Monitor for the following symptoms that require immediate medical attention: 2
- Difficulty breathing or chest pain 2
- Persistent high fever 2
- Decreased fetal movement 2
- Signs of preterm labor 2
Symptomatic Management
Concurrent symptomatic treatment is appropriate alongside oseltamivir: 1, 6
- Acetaminophen should be used for fever management 1
- Saline nasal rinses are safe and effective for nasal congestion 6
- Intranasal corticosteroids (budesonide, fluticasone, mometasone) are safe at the lowest effective dose 6
- Adequate hydration and rest are essential supportive measures 2
Medications to Avoid
- Phenylephrine should be avoided, especially in the first trimester, due to potential fetal risks including congenital malformations 6
- Oral decongestants should not be used, particularly during the first trimester 6
- Baloxavir marboxil is not recommended for pregnant women due to limited safety data 1, 8
Prevention for Future Pregnancies
All pregnant women should receive inactivated influenza vaccine (IIV) during any trimester, including the first trimester. 5, 1, 2