Will having the flu during your first trimester of pregnancy cause your baby to measure small?

Not likely.: Wrong dates is by far the most common reason for a small fetus in the first half of pregnancy. The influenza virus can cross the placenta and thus increase the risk of autism and schizophrenia in the offspring, if contracted during pregnancy. First trimester viral exposures generally follow the all or nothing rule - i.e. They either lead to miscarriage or do not affect the pregnancy. Talk with mfm.