Implications for the mother
Pregnant women, older people, the very young and those with a pre-existing health condition are at risk from the more serious effects of influenza infection.
Flu can cause intensive care admission for pregnant women.
One in 11 maternal deaths (36 pregnant women in the UK and Ireland) in 2009–12 was caused by certain strains of flu. There were two maternal death due to influenza in the last triennium (MBRRACE, 2019).
Implications for the fetus/neonate
Transplacental transmission of influenza virus is rare, yet still maternal influenza can have adverse effects on fetus.
Maternal infection during first trimester is associated with increased risk of spontaneous miscarriage and congenital anomalies (Luteijn et al, 2014).
There is growing evidence that influenza in pregnancy may lead to an increased risk of preterm labour and low birth weight.
In their paper, Irving et al (2000) found that despite influenza infection in the second and third trimesters of pregnancy being relatively common, there was no evidence for either transplacental transmission of influenza virus infection or for induction of potentially pathogenic auto antibodies. They felt this provided reassuring data concerning the likelihood of influenza induced abnormalities in fetal development.
In view of the potential maternal and fetal implications of influenza infection in pregnancy, Public Health England (PHE) and the World Health Organization (WHO) recommend annual influenza vaccination for all pregnant women. Epidemiological studies have shown that the influenza vaccine is safe during all stages of pregnancy including the first trimester. Pregnant women should be informed that the vaccine doesn't carry risks for either mother or fetus. In addition, pregnant women who have had the influenza vaccine pass some protection on to their babies, which lasts for the first few months of their lives. The vaccine also is safe for breastfeeding women and their babies.
Knight M, Bunch K, Tuffnell D, Shakespeare J, Kotnis R, Kenyon S, et al (Eds) on behalf of MBRRACE-UK. Saving Lives, Improving Mothers’ Care - Lessons Learned to Inform Maternity Care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2015-17. Oxford: National Perinatal Epidemiology Unit, University of Oxford 2019.
Knight M, Kenyon S, Brocklehurst P, Neilson J, Shakespeare J, Kurinczuk JJ (editors); on behalf of MBRRACE-UK. Saving Lives, Improving Mothers' Care. Surveillance of maternal deaths in the UK 2011-13 and lessons learned to inform future maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2009–12. Oxford: National Perinatal Epidemiology Unit, University of Oxford 2015.