Many adolescents planning on abstinence do not remain abstinent. As Dr. Hill wrote on the website healthychildren.org, “The best studies of adolescents who take a ‘virginity pledge’ suggest that these kids have sex just as early as those who don’t pledge, but that they are less likely to use birth control when they do have sex.”

Recognizing this, both the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists (ACOG) have urged their members to have “comprehensive” conversations with adolescent patients about their reproductive health and their contraceptive needs, knowledge and concerns.

Dr. Karen Gerancher, author of a recent ACOG opinion article on counseling adolescents about contraception, said, “When we’re able to reach patients before they become sexually active, or early in their sexually active life, we empower them to take control of their reproductive health, and prevent sexually transmitted infections and unintended pregnancies that could permanently impact the future they’ve envisioned for themselves.”

Although many adolescent girls choose birth control pills, as typically used they are not most effective in preventing pregnancy. Here’s what teens should know about contraceptive options, in order of effectiveness.

The implant. This long-acting reversible contraceptive is a matchstick-size flexible plastic rod that a doctor inserts under the skin, usually in the upper arm, where it can prevent pregnancy for at least three years, at which time it should be replaced. It contains a progestin hormone that blocks the release of an egg from the ovary. It is the most effective means of birth control, with a one-year failure rate significantly less than one in 100 (0.05 percent). Fertility typically returns quickly once the implant is removed.

An IUD. This other long-acting reversible contraceptive has a slightly higher failure rate of 0.2 to 0.8 percent. A doctor inserts the small T-shaped device into the uterus, where it prevents sperm from fertilizing an egg. There are two types: the Copper T IUD that has no hormone and needs to be replaced only once in 10 years, and a progestin-containing IUD that is replaced every three to five years.

Progestin injection. This shot of a progestin prevents the release of an egg from the ovaries for three months. Its failure rate is six in 100 within the first year.