Pregnancy and the Flu Shot

You're pregnant. For many women, pregnancy is a time of amazing changes, from thicker hair to burgeoning belly. The desire to nurture and protect your growing baby is instinctual and supplemented with advice from your obstetrician, the internet, and anyone who has even been pregnant. Never has human physiology and development been so interesting as when it is happening right before your eyes, in your very own body.

Much of the advice that women receive during pregnancy revolves around avoidance – avoid soft cheeses, hot tubs, over the counter medications. Avoid litter boxes, lunch meats, and steering wheels too close to Junior. Yet one thing pregnant women should not avoid is the inactivated, or attenuated, influenza vaccine. Anecdotally, many women feel healthier and note a reduction in serious illness during their second and third trimesters of pregnancy, but pregnancy conveys no protection against contracting influenza or the flu.

Exposure to the virus that causes influenza can be harmful to pregnant and post-pregnancy women for a number of reasons. First, women who contract influenza are more likely to develop significant illness and subsequent complications. Whether this is related to the bodily changes that occur during pregnancy – volume expansion, decreased lung capacity, increased oxygen consumption – or if this is a function of changed immunity patterns in pregnant women, it is not known why pregnant and recently pregnant women have higher mortality rates than non-pregnant women.

In addition, there can be fetal effects of maternal influenza including possible low birth weight, preterm delivery, increased rates of birth defects, and increased rates of spontaneous abortion. Yet infants whose mothers' did receive the flu vaccine have an added bonus of passive protection from their mother's immunoglobulin that is transferred across the placenta and through the breast milk during nursing.

However, many women harbor lingering concerns about the safety of the influenza vaccine, fears that may be remnants of a 2017 study that showed an association of increased first trimester miscarriage in pregnant women who had received a flu shot with the same strain coverage in years prior. While a cause and effect relationship was never established and the American College of Obstetricians and Gynecologists and the CDC continue to recommend influenza vaccine in any trimester of pregnancy, the rate of vaccination in pregnancy is still low, hovering around 50%.

If you are planning on becoming pregnant during influenza season, which is most associated with winter months in the northern hemisphere, make a plan to get your flu shot as part of your preconception care. If you find yourself pregnant as flu season begins, evidence supports healthier outcomes for your and your baby if you receive the influenza vaccine.