If the vaccines are only recommended for 16 yr olds and older, and the unborn child gets his/her immunity from the mother, it doesn't make any sense to give the vaccine to someone who is, or expects to be, pregnant.
It's an unknown risk, so prudence would dictate avoiding the vaccine prior to giving birth while being hyper-vigilant to do all the things we know reduces the chances of infection.
Aspirin was first created in 1853. A precursor for aspirin found in the Willow Tree has been used for 2,400 years. It took until 1986 for the FDA to recognize the risk of Reye's Syndrome in children to recommend that pregnant women in the last few months of pregnancy, children and teenagers avoid using aspirin.
COVID vaccines have had less than 2 years of clinical and field testing. Anyone who makes the statement "there's no evidence of long term effects causing birth defects," has no clue what "long term" means.