Hard to say. We know well that any virus that enters the blood (like flu) can pass to baby. How this affects baby is hard to say. Moms with a minor case will recover and may never have known they had flu. But some will have it so bad they die during pregnancy.An exposed fetus is not available for study during the pregnancy.
Media coverage was. given to one study from Denmark that showed a 3-fold increase in Autistic Spectrum Disorder in offspring of women who had the "flu" with fever for a week during pregnancy. No follow-up studies are available yet., but it is prudent to get a flu vaccine at least 2 months before conception or a flu shot, not the intranasal live virus, in the 2nd trimester if unprotected. .