What are the treatment options and potential risks for a pregnant woman who develops influenza during the first month of pregnancy?

Influenza in First Month of Pregnancy: Birth Defects and Treatment

Risk of Birth Defects

Influenza infection itself during the first trimester poses risks to fetal development, but treatment with oseltamivir does not increase the risk of birth defects and should be started immediately. 1, 2

Evidence on Birth Defects from Influenza Infection

• 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
• The teratogenic risk appears to stem from the infection itself (through direct viral effects or secondary effects like fever), not from antiviral treatment 3, 4
• Some data indicate an increased risk of birth defects in women infected with influenza during the first trimester, making prompt treatment critical 4

Safety of Antiviral Treatment in First Trimester

Multiple large studies demonstrate no association between oseltamivir use in the first trimester and birth defects:

• A CDC 5-year retrospective cohort of over 10,000 women found no association between first trimester influenza treatment and major congenital malformations 1, 2
• A systematic review and meta-analysis of 15 studies showed no association between congenital defects and influenza treatment in any trimester, including the first 1, 2
• Published studies of more than 5,000 women exposed to oseltamivir during pregnancy, including more than 1,000 women exposed in the first trimester, showed no increased rate of congenital malformations above the general population 5
• A population-based study from Denmark, Norway, Sweden, and France of 5,824 pregnant women (including 321 first trimester exposures to zanamivir) found no association with major birth defects, preterm birth, low birth weight, small for gestational age, stillbirth, neonatal morbidity, or neonatal mortality 6

Immediate Treatment Protocol

All pregnant women with suspected or confirmed influenza should receive oseltamivir 75 mg orally twice daily for 5 days, starting immediately without waiting for laboratory confirmation. 1, 2

First-Line Treatment

• Oseltamivir 75 mg orally twice daily for 5 days is the preferred first-line agent recommended by ACOG and CDC 1, 2, 7
• Treatment should begin as soon as possible after symptom onset, ideally within 48 hours, but should not be withheld if this window is missed 1, 7
• Do not wait for laboratory confirmation—treat presumptively based on clinical evaluation 1, 7
• Pregnancy is explicitly not a contraindication to oseltamivir use 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
• Zanamivir has limited systemic absorption but carries potential respiratory complications, particularly in women with underlying respiratory conditions 1

Managing Side Effects

• Take oseltamivir with food to significantly reduce nausea and vomiting (the most common side effects, occurring in approximately 10% and 9% of patients respectively) 1, 2
• Only 1% of patients discontinue treatment due to gastrointestinal side effects 1
• Use acetaminophen concurrently for fever management, as fever itself poses risks to fetal development 1, 8

Clinical Rationale for Aggressive Treatment

Pregnant women face dramatically elevated risks from influenza that far outweigh any theoretical medication concerns:

• Pregnant women are at higher risk for severe illness, pneumonia, ICU admission, and death compared to non-pregnant women 1, 2, 8
• The relative risk for hospitalization increases from 1.4 during weeks 14-20 of gestation to 4.7 during weeks 37-42 1, 2
• Treating influenza with oseltamivir may actually reduce fetal risk by shortening illness duration and reducing fever exposure 1

Warning Signs Requiring Urgent Evaluation

Monitor for these complications and seek immediate care if they develop:

• Difficulty breathing or chest pain 1, 2
• Persistent high fever 1, 2
• Decreased fetal movement 1, 2
• Signs of preterm labor 1, 2

Prevention for Future Pregnancies

• All pregnant women should receive inactivated influenza vaccine (IIV) during any trimester, including the first trimester 1, 2
• Vaccination can be administered as soon as seasonal vaccine becomes available, ideally by the end of October 2
• Live attenuated influenza vaccine (LAIV) is contraindicated during pregnancy 1, 2
• Vaccination protects both mother and infant, with infants born to vaccinated mothers having up to 72% risk reduction for laboratory-confirmed influenza hospitalization in the first few months of life 1, 2