This mixture of viruses is updated every year according to the current type of virus thought to be causing infection. It is necessary to receive the influenza vaccine each year in order to be protected from the current flu virus. The vaccine is given as an injection in the upper arm. Since the virus is inactivated, and the current data does not suggest an increased risk to the fetus, the influenza vaccine is considered safe for use during pregnancy. It is recommend that health-care providers consider giving the influenza vaccine to all women who will be in the second or third trimester of pregnancy or early postpartum during the influenza season.
Many experts do consider the influenza vaccine to be safe at any time during pregnancy.
However, due to the natural increased risk for miscarriage in the first trimester of pregnancy, it is recommended to avoid all unnecessary exposures during this time. Pregnant women who have medical conditions that increase their risk for complications from influenza should be vaccinated before the influenza season, regardless of the stage of pregnancy. If given in the third trimester, the vaccine may provide protection for the baby during its first few months of life because the mother can pass her antibodies to her baby through the placenta. A study looked at the incidence of birth defects, stillbirths, and intelligence in children whose mother's were and were not exposed to the vaccine while pregnant. The children were followed until they were seven years old and no differences were seen between the two groups.