The impact of Influenza infection during pregnancy

It is well established that some of the physiological changes that occur during pregnancy leave pregnant women and their growing baby at greater risk of serious influenza complications.

Influenza infection during pregnancy can have catastrophic consequences for both mother and baby including premature birth, stillbirth, small for gestational age and perinatal death.

Physiological changes during pregnancy that can lead to complications from influenza include the following:

  • Immune system: While humoral (antibody mediated) immunity appears to be enhanced, the cellular arm of the immune system is temporarily suppressed. This is to prevent harmful immune responses being directed at the growing baby, which is genetically foreign to the mother. These changes can leave a pregnant women more vulnerable to some intracellular pathogens including viral infections
  • Physical changes: Changes in the pelvic region, abdominal and thoracic cavities place pressure on surrounding organs. Lung capacity is decreased and oxygen consumption increased. Blood volume, heart rate and the amount of blood pumped per contraction (stroke volume) are increased

Risk to the women

Preliminary data from the SHIVERS hospital-based surveillance for severe acute respiratory infections in Auckland during 2012–2014 identified that pregnant women with influenza were five times more likely to be hospitalised than non-pregnant women.  A normally healthy woman who is pregnant has a similar risk for complications from influenza as nonpregnant women who have co-morbidities. This risk increases with gestation. When pre-existing medical conditions are superimposed on pregnancy the risks become even higher.

Evidence suggests that pregnant women are even more vulnerable during pandemics.

Risk to the growing baby

Direct vertical transmission of the influenza virus to the growing baby is thought to be extremely rare. The adverse effects observed on the baby in mothers who have influenza are likely to be indirect
i.e. as a result of the mother’s response to the virus. Maternal influenza infection can be associated with congenital abnormalities caused by fever. Overall there is an increase of general pregnancy
complications in women who have influenza.

Historical studies proposed a possible link between maternal influenza infection during pregnancy and an increased risk of cancer in infants and children, such as leukaemia after the 1957 influenza
pandemic, brain tumours or neuroblastomas. The increased risk of cancer in a child born to a mother who had influenza during pregnancy was extremely low as these are rare cancers.

Risk for goung babies

Babies less than 6 months of age have a higher risk of being hospitalised with influenza than other age groups.69,70,93 Influenza related complications can include fever related convulsions, vomiting
and diarrhea, pneumonia and occasionally brain inflammation.

In Auckland during 2015, infants aged less than 1 year had the highest rate of hospitalisation with a severe acute influenza respiratory infection than all other age groups, 289 cases per 100,000 people
compared with 20/100,000 midlife adults and 141/100,000 adults aged 80 years or older.

Vaccination and Breastfeeding

The influenza vaccine can be given to a breastfeeding woman. Protecting the mother can help prevent her becoming infected and transmitting influenza to her baby. Breastfeeding may offer some protection against influenza.