IN MANY CASES, even when a teen is aware of the risks when she becomes sexually active, pregnancy is a surprise. How a girl learns she is pregnant—and the kinds of stress she endures in breaking the news to her family, as well as to the father of the baby—is often traumatic.

Finding out by accident

For many teens who have tried to minimize the risk of pregnancy, the early physical indications that they are pregnant are so unexpected, so subtle, that they are completely ignored. Being overly tired or feeling bloated or nauseated can be chalked up to a number of ailments— from the flu to premenstrual cramping. Health care professionals are often bewildered when girls come in several months pregnant without any knowledge of what is happening to them. In many...