Immunization during pregnancy reduces the risk of miscarriages, stillbirths, low birthweight, and premature deliveries

Studies from multiple Western countries have found that pregnant women infected with influenza during the 2009 A/H1N1 pandemic were at higher risk of miscarriages, stillbirths, low birthweight and premature deliveries. The risk of fetal death was between 2 and 5.5 times higher in pregnant women with influenza than in pregnant women without influenza. In the UK, the rate of stillbirths was 4.5 times higher and the likelihood of preterm delivery was 4 times greater in influenza-infected pregnant women than non-infected women.

Although this article indicated that influenza vaccination is safely used for the mother and the fetus, conflicting data exists on the effect of vaccination in improving preterm birth rates.