In an open adoption, the birth mother meets and chooses the adoptive family and there is contact throughout the pregnancy. The birth mother may choose to allow the adoptive mother to accompany the birthmother to all of her prenatal appointments and may even invite her to be present in the room when the baby is delivered. In an open adoption, there is usually some level of contact after the adoption, often a letter with pictures once a year, as the adoptive parents are willing.
In a closed adoption, the birth mother does not meet the adoptive family and does not ever know their identity. There is no contact after birth.