However, even this does not offer a long-term solution if there is no social service intervention to help girls appreciate the value of contraception, says author Catherine Stevens-Simon, M.D., of the University of Colorado Health Sciences Center and The Children's Hospital.
"We suspect that these contraceptives are uniquely effective with teenagers because they are currently the only methods that make the default (do-nothing) position as nonpregnant (rather than pregnant)," she and her co-investigators explain.
The study is published in the July issue of American Journal of Preventive Medicine.
Stevens-Simon and her colleagues looked at pregnancy rates in 350 girls participating in the Colorado Adolescent Maternity Program, which covered prenatal and postnatal care and emphasized healthy habits, consistent contraceptive use, regular school attendance and planning for the future.
As part of the program, the teens were encouraged to choose a birth control method during the period after their delivery and before they became fertile again.
One year after delivery, none of the girls who had chosen Norplant, a slow-release hormonal contraceptive that is implanted under the skin and lasts four to five years, was pregnant.
In contrast, 11 percent of those who started on Depo-Provera, a hormone injection whose effects last about three months, became pregnant in the first year. Twenty-five percent of those who decided to use oral contraceptives and 38 percent of those who decided against birth control became pregnant.
"Despite guaranteed access to equally effective contraceptives and strong encouragement to use them, many former Depo-Provera and pill users became pregnant again. By contrast, 12 months postpartum, 90 percent of Norplant users were still using this method and none was pregnant," the investigators say.
Of the 286 girls who were still participating in the program at two years 35 percent had become pregnant again: 11 percent of those who had started on Norplant, 31 percent of those who initially chose Depo-Provera, 51 percent of those taking oral contraceptives and 65 percent of those using no birth control.
Second pregnancies were not the result of birth-control failure, but were due to the teens discontinuing use of their chosen birth control method. In the case of Norplant, this means they had the implant removed.
The researchers note that high attrition rates from this and other teen parenting programs suggest that many of these girls do not place a high value on the type of help these programs offer. For many teen parents the costs of pregnancy do not outweigh the costs of using contraceptives particularly when they cause inconvenient side effects.
Stevens-Simon adds that interventions should be able to reverse these feelings.
"We do not see the prevention of closely spaced adolescent pregnancies as an end in itself. Rather, we recommend that long-acting contraceptive agents be used to buy the time healthcare and social service providers need to create villages in which the real life costs of conception outweigh the costs of contraceptive use for the majority of adolescent parents," they say.
The study was funded by the National Center for Research Resources, a part of the National Institutes of Health.
The American Journal of Preventive Medicine, sponsored by the Association of Teachers of Preventive Medicine and the American College of Preventive Medicine, is published eight times a year by Elsevier Science. The Journal is a forum for the communication of information, knowledge and wisdom in prevention science, education, practice and policy. For more information about the Journal, contact the editorial office at (619) 594-7344.
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