Decades ago, virtually all adoptions were closed. A closed adoption means that there is no contact whatsoever between the birthparents and the adoptive parents and child after the adoption takes place. In fact, there may also be no contact before the adoption. Nowadays, however, the trend in the United States is toward open adoptions, in which all the parties to an adoption meet and often remain in each other's lives.
Historically, the four primary reasons for married couples to obtain a child via closed adoption have been (in no particular order) infertility, asexuality, having concern for a child's welfare (i.e. would not likely be adopted by others), and to ensure the sex of the child (a family with five girls and no boys, for example). In 1917, Minnesota was the first U.S. state to pass an adoption confidentiality and sealed records law. Within the next few decades, most United States states and Canadian provinces had a similar law. Usually, the reason for sealing records and carrying out closed adoptions is said to be to "protect" the adoptee and adoptive parents from disruption by the natural parents and in turn, to allow natural parents to make a new life.
In all adoption searches, it is uncommon to find both the birth mother and father at the same time. A separate search, if desired, can be done afterwards for the father. Since males seldom change their surnames, and the mother might have additional information, it is usually easier than the initial search for the birth mother. In many cases, adoptees are able to do this second search for their birth father by themselves (or they try before paying for assistance).