Have your sponsor contact the U.S. Citizenship and Immigration Services (USCIS) service center where your petition for immigration was submitted, if the petition has not yet been approved. Your sponsor can inform the USCIS of your newborn and your intention to have your child immigrate to the United States with you. Because you are considered the beneficiary of the petition your sponsor submitted, your newborn will be considered a "derivative beneficiary."
Have your sponsor contact the National Visa Center (NVC) if your petition has been approved to inform them of your newborn. The NVC is located in Portsmouth, New Hampshire, and processes all approved immigrant visa petitions after they have been received from the USCIS. Your petition remains with the NVC until it is ready for adjudication by a consular officer in your country. Depending on the category of your immigrant visa application, your petition may remain with the NVC for several months or even years.
Inform the consular officer at your application interview about your newborn, if you have already received your consular interview instruction packet from the NVC. Once you have received this notification, your case is ready for adjudication by an embassy consular officer and he will handle all issues related to your application at this point.