Treatment of Influenza in Pregnancy
Pregnant women with suspected or confirmed influenza should receive immediate antiviral treatment with oseltamivir 75 mg orally twice daily for 5 days, regardless of vaccination status, trimester, or time since symptom onset. 1, 2, 3
Immediate Treatment Protocol
- Start oseltamivir presumptively based on clinical symptoms alone—do not wait for laboratory confirmation or test results 2, 3
- Treatment is most effective within 48 hours of symptom onset, but should never be withheld even if this window has passed 2
- The standard adult dosing of oseltamivir 75 mg orally twice daily for 5 days applies to all trimesters of pregnancy 1, 4
- Over-the-phone prescribing for low-risk patients is preferred to reduce disease transmission in clinical settings 2
Alternative Antiviral Option
- Zanamivir 10 mg (two 5 mg inhalations) twice daily for 5 days can be used if oseltamivir is contraindicated 1
- Zanamivir is not recommended for pregnant women with underlying asthma or chronic obstructive pulmonary disease due to bronchospasm risk 5
- For pregnant women with asthma or heart disease, oseltamivir remains the preferred agent 1, 5
Clinical Rationale for Aggressive Treatment
Pregnancy dramatically increases influenza-related morbidity and mortality through multiple mechanisms:
- The relative risk for hospitalization escalates from 1.4 at weeks 14-20 of gestation to 4.7 at weeks 37-42 compared to postpartum women 6, 1
- Third-trimester pregnant women have hospitalization rates (250/100,000) comparable to non-pregnant individuals with high-risk medical conditions 6
- Physiologic changes in pregnancy increase vulnerability: elevated heart rate and stroke volume, increased oxygen consumption, decreased lung capacity, and altered immunologic function 6, 1
- Pregnant women with underlying conditions like asthma or heart disease face even higher risks and require treatment regardless of trimester 6
Fetal and Pregnancy Complications
- Influenza infection during pregnancy increases odds of congenital anomalies, stillbirth, late pregnancy loss, preterm delivery, low birth weight, and small-for-gestational-age infants 1, 7
- Historical pandemic data (1918-19 and 1957-58) documented disproportionately high maternal mortality rates 6, 1
Safety Profile of Oseltamivir in Pregnancy
- Studies of over 2,000 pregnant women demonstrated no adverse fetal effects from oseltamivir 6, 1
- No association exists between first-trimester oseltamivir exposure and major congenital malformations 1
- The most common side effects are nausea (10%) and vomiting (9%), which are generally well-tolerated 1
- The benefits of treatment far outweigh any theoretical risks at any stage of pregnancy 2, 7
Post-Exposure Prophylaxis
- Antiviral chemoprophylaxis can be considered for pregnant women up to 2 weeks postpartum who have had close contact with infectious individuals 2
- Prophylaxis dosing: oseltamivir 75 mg once daily for 7-10 days following exposure 4
- This is particularly important for unvaccinated pregnant women during pandemic settings 7
Warning Signs Requiring Urgent Evaluation
Monitor pregnant patients for the following red flags that necessitate immediate assessment:
- Difficulty breathing or shortness of breath 1
- Chest pain or pressure 1
- Persistent high fever despite acetaminophen 1
- Decreased fetal movement 1
- Signs of preterm labor 1
Critical Pitfalls to Avoid
- Never delay treatment waiting for laboratory confirmation—clinical suspicion alone warrants immediate oseltamivir 2, 3
- Never withhold treatment because the 48-hour window has passed—late treatment still provides benefit 2
- Never let vaccination status influence the decision to treat—vaccinated pregnant women with breakthrough infections still require antivirals 2, 3
- Avoid aspirin for fever control in pregnancy due to Reye syndrome risk; use acetaminophen instead 1
- Do not prescribe live attenuated influenza vaccine (LAIV) during pregnancy—only inactivated vaccines are appropriate 1, 8