Sarah burying her head in the sand. If Adam is not the dad, it is bound to come out sometime, if the baby is ill and needs a blood transfusion or transplant, it could come out that his blood group does not match with Adam. A well used Soap trope.
P.S. I have always wondered how people quote more than one post, and here, I have done it without meaning to, and do not know how I did it.