No effect at all - at least not a negative one. Regardless of the day the baby was born in 2017, when listing them as your dependent on your tax return, you will select the option to indicate the baby lived with you THE ENTIRE YEAR. Doesn't matter if the baby was born at 11:59pm on New Year's Eve. The IRS says you claim them for the entire tax year. This is going to automatically exempt an additional $4,050 of your income from being taxed, and it should be a bit of a help for you on the financial front with what it costs for diapers now-a-days.
