The effects of influenza on pregnancy

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The effects of influenza on pregnancy

• Pat OBrien

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Seasonal flu

• A respiratory illness ? No viraemia
• No transplacental transmission
• Fetal abnormalities very unlikely
• 11 of all mothers have proven infection
• More complications of pregnancy
• HT, bleeding, breech!
• No single complication significantly ?
• Pregnancy outcomes are the same
• Ramphal et
  al, AJOG, 1980
• 
  Irving et al, BJOG, 2000

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Pandemic flu

• More invasive and more virulent
• Viraemia common
• ? Possibly reaches placenta /- fetus
• Evidence lacking

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Pregnancy and H5N1 infection

• Case report Gu et al, Lancet,
  2007 (post-mortem pregnant woman)
• Virus detected in placenta and fetus
• Lungs, liver macrophages, circulating monocytes
• Mild acute interstitial pneumonitis
• Why the difference?
• Maternal viraemia more common
• Different virus receptor expression
• Lungs
• High number of infected cells, but
• No evidence of severe damage
• ? Due to naive immune status (less cytokines)

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Effect on baby virus(if transplacental spread)

• 1st trimester
• Miscarriage/birth defects
• 2nd trimester
• Miscarriage/IUFD
• ? Neuropsychiatric morbidity
• Japan 1957 flu in 2nd trimester
  ? risk of schizophrenia in children ? x 3
• Close to delivery
• Neonatal influenza infection

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Effect on fetus - fever

• Uncertain (epidemiological studies), but...
• Episodes of hyperthermia common
• 18 in 1st trimester
• Miscarriage
• No Andersen et al, Lancet, 2002
• Yes (OR 5.5) Kline et al, Am J Epid, 1985
• Fetal abnormalities
• Animals Yes (Brain, NTD, clefts, heart)
• Edwards, Birth
  Defects Research, 2006
• Humans Perhaps (NTD, heart)
• Milunsky et al, JAMA,
  1992
• Tikkanen et al,
  Eur J Epid, 1991

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Effect on fetus maternal condition

• Severe maternal illness
• hypoxia
• hypotension
• Hypoxia pyrexia
• ? increased risk of hypoxic brain damage

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Any evidence from previous flu
pandemics?

• Little good evidence
• Stillbirth figures from past 80 years
• No changes that could be attributed to pandemic
  flu

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Effect on mother

• Viral pneumonia
• /- secondary bacterial pneumonia
• Are pregnant women more susceptible to seasonal
  flu virus?
• Evidence conflicting, but probably yes
• CDC believes so ? recommends vaccination

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Effect on mother

• Is seasonal flu pneumonia more severe/fatal in
  pregnant women?
• Again, evidence conflicting, but probably yes
• Chickenpox pneumonia case fatality rate ? x 5
• 3rd trimester
• ? immune function Likely to ?
  respiratory
• ? body water dysfunction caused by
• Splinting of diaphragm pneumonia

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Effect of pandemic flu virus on mother

• 500,000 women pregnant
• 250,000 infected
• 2.5 case fatality rate
• 6,250 maternal deaths
• Maternal mortality rate
• 1.25
• 1250 per 100,000
• (not counting deaths in puerperium)

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H1N1 Swine Flu - Australia

• Population 21 million
• 27,000 cases
• 95 deaths (1 in 20,000)
• 3,281 hospital admissions
• 1918-9 pandemic 1 in 400 died
• More seriously affected
• Pregnant
• Obese
• Diabetes

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H1N1 Swine Flu

• DH/RCOG recommends
• Do not need to take swabs
• Do not give post-exposure prophylaxis
• Do treat pregnant women with flu symptoms
• Choice of drug
• Zanamivir (Relenza) in pregnancy
• Severe Asthma ? consider using Tamiflu
• Encourage breast-feeding (use Tamiflu)

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Key messages

• Paradox most mild, but some very severe
• Younger age group
• Obese, pregnant, diabetes
• Treat pregnant women
• DONT PANIC! But dont be complacent

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Next steps

• Second wave
• Resistance
• Genetic re-assortment or recombination
• Vaccination
• High risk groups
• Front-line staff
• Mechanism

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