So if you left your taxes as is with 0 dependents, then you would just receive a larger refund at the end of the year. However, I know that many people like to receive more money on each check rather than a larger refund. In order to do this, then you would need to fill out a new W-4 form with your employer. The IRS has updated the W-4 form and it is easier now to fill out. Step 3 is where you would account for the new little one.
However, the best way to get a good estimate is to use the IRS tax-withholding estimator at https://www.irs.gov/individuals/tax-withholding-estimator. This tool is amazing and you can really calculate how much based on what you have made this year and your situation that you need to adjust to receive the refund you want.