Dear Tracer,

Thank you for this good question. sciences of gynecology, obstetrics, pediatrics, reproductive health, etc show that mothers and fetus share the same life during pregnancy.  check these links for your answers:

https://www.babycenter.com/0_the-dtap-vaccine_1563.bc

http://www.vaccinationcouncil.org/2011/06/01/vaccines-and-brain-inflammation/

https://www.cdc.gov/mmwr/pdf/rr/rr4512.pdf

https://wicworks.fns.usda.gov/wicworks/Topics/Vaccines101Guide.pdf

http://www.jogc.com/article/S1701-2163(16)30416-9/pdf

Good luck

Great question! The biggest problem is maternal fever. Influenza infection causes maternal fever, and thus, a big problem for in utero development. Flu vaccination prevents that, and that is why it is very important to vaccinate pregnant women against influenza. I've participated in studies with over 10000 pregnant patients receiving influenza vaccines, and no teratogenic effect was ever seen.