Flu-season immune support: third trimester

By trimester

Weeks 28–birth

3rd trimester

A flu shot in the third trimester passes protective antibodies to your baby, covering them for the first several months before they're old enough for their own vaccines. Call your provider sooner rather than later if you get any respiratory illness this late in pregnancy.

What does the evidence show for flu-season immune support?

• Babies whose mothers got a flu shot during pregnancy have fewer flu hospitalizations and emergency-room visits before they turn 6 months old. 1
• The flu shot is recommended in any trimester, and getting it early in the third trimester works well alongside other pregnancy vaccines, like the RSV vaccine and Tdap, when you're scheduling several at once. 2
• Pregnant people are more likely than other adults to get seriously sick from the flu, especially in the third trimester when there's simply less room to breathe deeply. 3
• No single supplement has proven pregnancy-specific benefit against respiratory infections, so it's best to talk to your provider before adding any new supplement in the third trimester rather than deciding on your own. 4
• Pregnancy sits among the high-risk groups for severe influenza, where illness can escalate to breathing difficulty, a fast heart rate, and low blood pressure inside 48 hours, and where primary viral pneumonia and secondary bacterial pneumonia are the complications of concern. 5

When should I call my provider about flu-season immune support?

Everything on this page is about hygiene, rest, and vaccination, none of which is a plan for riding out a serious infection at home in the last trimester. Call the same day if a respiratory illness brings shortness of breath, a racing heart, or lightheadedness, because pregnancy is a named high-risk group and severe influenza can build within about 48 hours. The improve-then-worsen pattern with a returning fever suggests bacterial pneumonia settling in behind the virus. No supplement changes that calculus: a fever or a breathing symptom this late is a provider call, not a supplement decision. If you are ever unsure which side of the line you are on, make the call. Obstetric teams handle these check-ins as routine, not as overreacting.