Around 4 million babies are born in the United States each year. Of non-stepparent adoptions, about 59 percent are from the child welfare (or foster) system, 26 percent are from other countries, and 15 percent are voluntarily relinquished American babies.
There's nothing shameful about adoption. Families should celebrate the adoption of a baby as they would celebrate a birth, with announcements, baby showers, etc. They should also encourage a child to be proud of his/her birth culture, as well as to accept the culture of his/her adoptive family.
That being said, adoption is an event in a baby's life. It does not define the baby. There is no reason to mention that a baby was adopted unless it is relevant to what is being discussed.
