What are the risks of having influenza in the first few weeks of gestation?

Risks of Influenza in Early Pregnancy

Influenza infection in the first few weeks of gestation poses a lower risk compared to later pregnancy stages, but pregnant women should still be monitored closely as physiological changes in pregnancy can increase susceptibility to complications.

Risk Assessment by Trimester

The risk of influenza complications increases progressively throughout pregnancy:

• First trimester (< 14 weeks):

  • Lower relative risk compared to later pregnancy
  • Relative risk for hospitalization for cardiorespiratory conditions: approximately 1.4 compared to non-pregnant women 1

• Second trimester (14-20 weeks):

  • Moderate increase in risk
  • Relative risk for hospitalization: approximately 1.4 compared to non-pregnant women 1

• Third trimester (especially weeks 37-42):

  • Highest risk period
  • Relative risk for hospitalization: 4.7 compared to non-pregnant women
  • Hospitalization rate comparable to non-pregnant women with high-risk medical conditions 1

Physiological Mechanisms for Increased Risk

Several pregnancy-related changes contribute to increased influenza susceptibility:

• Cardiovascular changes:

  • Increases in heart rate and stroke volume 1
  • Increased oxygen consumption 1

• Respiratory changes:

  • Decreased lung capacity 1

• Immunological changes:

  • Alterations in immune function 1

Potential Complications

While the risk is lower in early pregnancy compared to later stages, potential complications include:

• Maternal complications:

  • Increased risk of hospitalization 1
  • Potential for severe respiratory illness 2, 3
  • Pneumonia 4, 5

• Pregnancy/fetal complications:

  • Potential increased risk of miscarriage (though data is limited for first trimester specifically) 2, 3
  • Potential for preterm delivery if infection is severe 2, 5, 3
  • Small-for-gestational age infants 2

Prevention and Management

For women in early pregnancy:

• Vaccination:

  • Vaccination is the most effective prevention strategy 1, 2
  • While some experts prefer vaccination after the first trimester to avoid coincidental association with spontaneous abortion (which is common in first trimester), the inactivated influenza vaccine is considered safe during any stage of pregnancy 1
  • Pregnant women with pre-existing medical conditions that increase risk should be vaccinated regardless of gestational age 1

• Antiviral treatment:

  • Early treatment with oseltamivir is recommended for pregnant women with suspected or confirmed influenza 2, 4, 3
  • Prompt treatment can reduce risk of complications and attenuate potential teratogenic effects of influenza infection 2

Important Considerations

• Historical context: Excess mortality among pregnant women has been documented during influenza pandemics (1918-1919 and 1957-1958), though not during interpandemic periods 1

• Household contacts: Vaccination of household contacts and caregivers is recommended to provide additional protection 1

• Monitoring: Close monitoring of pregnant women with influenza symptoms is essential, even in early pregnancy, as complications can develop rapidly 4, 6

Conclusion

While the risk of complications from influenza is lower in the first few weeks of gestation compared to later pregnancy stages, the physiological changes of pregnancy begin early and can increase susceptibility to complications. Early recognition, vaccination (when appropriate), and prompt treatment are essential to minimize risks to both mother and developing fetus.