Endocrine Abstracts

Previous studies of the injectable contraceptive depot medroxyprogesterone acetate (DMPA, Depo-Provera) and bone mineral density have produced differing results; a bone mineral deficit has been demonstrated in studies of the lumbar spine and hip, but not in studies of the forearm. In addition, DMPA users are likely to be smokers, pregnant at a young age, and not educated beyond high school level, which could contribute to the observed bone density deficit.

This study aims to determine the effect of DMPA on the skeleton of young adult women, and to eliminate the effect of social and lifestyle factors by the use of individually matched controls. The study was approved by the local Ethics Committee.

We recruited 50 pairs of women ages 18 to 25 from Sheffield general practices and family planning clinics. DMPA use was of at least 12 months duration (mean 37 months), and commenced before the age of 20. Controls were matched for source of recruitment, postcode, age, height, body mass index and smoking habit. We included users of the combined oral contraceptive in the control group, as there is good evidence it has no effect on bone mineral density, and is the commonest contraceptive choice in this population.

Bone mineral density was assessed by dual x-ray absorptiometry at the spine, hip (Hologic Delphi) and forearm (Osteometer DTX 200).

Paired t-test showed a bone density deficit of 5.6% at the spine (95%CI: -9.3 to -1.9%) and 5.2% at the hip (95%CI: -9.4 to -0.92%) in DMPA users, but no difference at the forearm.

The site-specific effect is unexpected, as post-menopausal sex steroid deficiency affects the spine, hip and forearm, and it may be that DMPA as a progestogen has a protective effect at the forearm. Studies which have examined forearm bone density alone may be falsely reassuring.