Bone mineral density in adolescent females using injectable or oral contraceptives: a 24-month prospective study.

OBJECTIVE: To determine whether bone mineral density (BMD) is lower in hormonal-contraceptive users than in an untreated comparison group.

DESIGN: Observational, prospective cohort; 24-month duration.

SETTING: Adolescent clinics in a metropolitan Midwestern setting.

PATIENT(S): Four hundred thirty-three postmenarcheal girls, 12-18 years of age, who were on depot medroxyprogesterone acetate (DMPA; n = 58), were on oral contraceptives (OCs; n = 187), or were untreated (n = 188).

INTERVENTION(S): Depot medroxyprogesterone acetate and OCs containing 100 microg of levonorgestrel and 20 microg of ethinyl E(2).

MAIN OUTCOME MEASURE(S): Measurements of BMD at spine and femoral neck were obtained by using dual x-ray absorptiometry at baseline and 6-month intervals.

RESULT(S): Over 24 months, mean percentage change in spine BMD was as follows: DMPA, -1.5%; OC, +4.2%; and untreated, +6.3%. Mean percentage change in femoral neck BMD was as follows: DMPA, -5.2%; OC, +3.0%; and untreated, +3.8%. Statistical significance was found between the DMPA group and the other two groups. In the DMPA group, mean percentage change in spine BMD over the first 12 months was -1.4%; the rate of change slowed to -0.1% over the second 12 months. No bone density loss reached the level of osteopenia.

CONCLUSION(S): Adolescent girls receiving DMPA had significant loss in BMD, compared with bone gain in the OC and untreated group. However, the clinical significance of this finding is mitigated by slowed loss after the 1st year of DMPA use and general maintenance of bone density values within the normal range in the DMPA group.