Welcome to the board! Yes, it is possible to adopt a new-born and not have post placement contact with birthparents. I have two friends who were called to the hospital to adopt their children just after they were born. Both birthmoms wanted no contact with the family or the children after that.
Also, I was contacted by 3 different potential birthmoms (with verified pregnancies). Two of them initially thought they would want no contact after the baby was placed. And one wanted updates and an annual visit. The latter had placed a baby before with a family who lives in her city and enjoys a very open relationship--we live across the country from her so our situation would have been very different. Ultimately she suspended her search for an adoptive family due to some drama with her husband. We have since matched with one of the women who initially thought she wouldn't want contact, but since we have been getting to know each other over the past month, I think she is opening up to the idea of a more open arrangement. She lives in another state so we won't be visiting every weekend.
My own sister adopted both her children one in the 80s and one in the 90s. One of her birthmoms does contact her to chat on the phone, but she has never spoken with my nephew. My sister sends her pics and updates fairly regularly. THe other birthparents really don't have that much interest in maintaining contact or even getting updates though they said they would be open to meeting with my niece if she wants to know them after she turns 18.
My point in telling you all this is just to let you know that there are potential birthmoms out there who don't necessarily want contact after placement, but most do want to meet you before choosing you so that they can feel confident of their decision to place with you. When their is no contact or limited contact arranged through an agency, it is usually considered a semi-open adoption.