Can I get a deduction or credit if I was pregnant in 2023 but didn’t have baby until 2024?

Not for tax year 2023.

You can only claim your child (for child tax credit and EIC purposes) starting the year he/she is born. For the birth year, he/she is considered as having lived with you the whole year.

There is one state---Georgia--- in which you can get a state credit if you were pregnant in 2023.   Otherwise--you wait until next year after your child has been born in 2024 and claim your child as a dependent on a 2024 tax return.