What to do if your expecting baby how can i add new baby as a dependant

You cannot claim a new baby as a dependent until after the baby is born.  If the birth is on December 31 or earlier you can claim the baby for the entire year. 

You cannot add your child as a dependent unless the child was

born in 2019.  

Next year, when your child has actually been born and you have a Social Security number for your child, you can claim your child on your 2020 tax return.