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Which Trimester Is Best to Get the Flu Shot?

A new study says the flu shot's effectiveness for a pregnant woman may depend on which trimester she's in.

pregnant woman getting vaccine in doctors office Ariel Skelley/Getty Images
According to the Centers for Disease Control, flu is more likely to cause severe illness in pregnant women than in healthy women who are not pregnant. Which is why the organization recommends all pregnant women get vaccinated, unless they've already recevied a shot during the last year.

As for when during your pregnancy is the best time to get a flu shot, the CDC says it's safe during any trimester. But a recent study found that the effectiveness of the shot depends on the trimester in which the woman receives it.

Researchers studied 36 pregnant women during flu season from 2012 to 2014. They administered inactivated influenza vaccine, and collected blood samples pre-vaccination, then again 14 days later. They found that the body's response varied based on the trimester in which the shot was given—and that it appeared to have the greatest response when given in the first trimester.

The results suggest immunologic changes that occur during pregnancy may affect response to vaccination, according to Emily Patel, M.D., one of the researchers and the presenter of the study. "Future studies will lead to a better understanding of vaccine immunology and how pregnant women respond to antigen exposure through the course of their pregnancy," she added.

Hollee Actman Becker is a freelance writer, blogger, and a mom. Check out her website holleeactmanbecker.com for more, and follow her on Twitter at @holleewoodworld.