What is the recommended management for influenza in pregnant women?

Management of Influenza in Pregnancy

All pregnant women with suspected or confirmed influenza should immediately receive oseltamivir 75 mg orally twice daily for 5 days, starting treatment without waiting for laboratory confirmation, regardless of trimester, vaccination status, or time since symptom onset. 1, 2, 3

Immediate Antiviral Treatment

First-Line Therapy

• Oseltamivir (Tamiflu) is the preferred antiviral agent: 75 mg orally twice daily for 5 days 1, 2, 3
• Treatment should begin immediately upon clinical suspicion—do not wait for laboratory confirmation or test results 2, 3
• While treatment within 48 hours of symptom onset is ideal, do not withhold treatment if this window has passed, as pregnant women remain at high risk for complications even with delayed treatment 3
• Taking oseltamivir with food significantly reduces the most common side effects of nausea (10%) and vomiting (9%) 2

Alternative Therapy

• Zanamivir 10 mg (two 5 mg inhalations) twice daily for 5 days can be used if oseltamivir is contraindicated or unavailable 1, 2
• Zanamivir has limited systemic absorption but carries potential respiratory complications, particularly in women with underlying respiratory conditions 2

Safety Profile in Pregnancy

• The FDA classifies oseltamivir as Pregnancy Category C, but extensive post-marketing surveillance demonstrates reassuring safety outcomes 2
• No adverse effects have been reported among women who received oseltamivir during pregnancy or among their infants 2
• Available data from published studies suggest that use of zanamivir during pregnancy is not associated with an increased risk of birth defects or adverse maternal or fetal outcomes 4
• Only 1% of patients discontinue oseltamivir treatment due to gastrointestinal side effects 2

Clinical Rationale for Aggressive Treatment

Maternal Risks

• Pregnant women face 7.2 times higher hospitalization rates compared to non-pregnant women during influenza pandemics 5
• The relative risk for hospitalization increases dramatically throughout pregnancy: from 1.4 during weeks 14-20 to 4.7 during weeks 37-42 1, 2
• Pregnant women are at higher risk for severe illness, pneumonia, ICU admission, and death compared to non-pregnant women 1, 2

Fetal and Pregnancy Risks

• Influenza infection during pregnancy is associated with late pregnancy loss (adjusted hazard ratio 10.7; 95% CI 4.3-27.0) 5
• Additional risks include congenital anomalies, stillbirth, preterm delivery, low birth weight, and small-for-gestational-age infants 1, 2
• Fever itself poses risks to fetal development, so treating influenza with oseltamivir may actually reduce fetal risk by shortening illness duration 2

Post-Exposure Prophylaxis

High-Risk and Moderate-Risk Exposure

• Oseltamivir 75 mg once daily for 7-10 days after last known exposure is recommended for pregnant women with close contact to infectious individuals 2
• The CDC advises that postexposure antiviral chemoprophylaxis can be considered for pregnant women and women up to 2 weeks postpartum (including after pregnancy loss) 3

Influenza Vaccination During Pregnancy

Universal Recommendation

• All pregnant women should receive inactivated influenza vaccine (IIV) during any trimester, including the first trimester 5, 1
• The CDC and WHO recommend that pregnant women be prioritized to receive the seasonal influenza vaccine all year round 5
• Vaccination should be administered as soon as the seasonal vaccine becomes available, ideally by the end of October 1

Vaccine Types

• Inactivated influenza vaccine (trivalent or quadrivalent) is safe and recommended during pregnancy 5
• Live attenuated influenza vaccine (LAIV) is contraindicated during pregnancy due to theoretical risk of placental transmission of virus to the fetus 5, 1
• Any licensed, age-appropriate inactivated influenza vaccine (IIV3 or IIV4) or recombinant influenza vaccine (RIV3 or RIV4) may be used 1

Safety in First Trimester

• No association between first trimester influenza vaccination and major congenital malformations was found in a 5-year retrospective cohort of over 10,000 women 1, 2
• A systematic review and meta-analysis of 15 studies showed no association between congenital defects and influenza vaccination in any trimester 1, 2

Maternal and Infant Protection

• Infants born to vaccinated mothers have a 72% risk reduction for laboratory-confirmed influenza hospitalization in the first few months of life 1, 6
• Vaccination provides dual protection: transplacental antibody transfer during pregnancy (IgG) and breast milk transfer of antibodies (IgA) after birth 6
• Pregnant women in their third trimester should receive vaccination during July-August when vaccine first becomes available, as this maximizes infant protection through transplacental antibody transfer 1, 6

Warning Signs Requiring Urgent Evaluation

Monitor pregnant women with influenza for the following complications requiring immediate assessment: 1

• Difficulty breathing or chest pain
• Persistent high fever
• Decreased fetal movement
• Signs of preterm labor

Common Pitfalls to Avoid

• Do not delay treatment waiting for laboratory confirmation—treat based on clinical suspicion 2, 3
• Do not withhold treatment beyond 48 hours of symptom onset—late treatment still provides benefit in pregnant women 3
• Do not use live attenuated influenza vaccine (nasal spray) during pregnancy—only inactivated vaccines are safe 5, 1
• Do not postpone vaccination due to first trimester concerns—extensive safety data supports vaccination in all trimesters 1, 2
• Do not use over-the-phone assessment as a reason to avoid treatment—the CDC actually recommends over-the-phone treatment for low-risk patients to reduce disease spread 3