Bone mineral density and depot medroxyprogesterone acetate

Depot medroxyprogesterone acetate (DMPA) suppresses pituitary gonadotrophin output, thus, suppressing ovulation. Estrogen production from the ovary is also strongly inhibited, and the resulting estrogen deficiency has a detrimental impact on bone. Depot medroxyprogesterone acetate may be particularly detrimental in young women, as it may impede attainment of peak bone mass, and switching to a different contraceptive is recommended. However, the effect of sequential use of DMPA with other contraceptives in this age group has not been investigated.

This was a cross-sectional analysis of 218 DMPA users who were 20 years or older (mean, 31 years, +/-8.9 SD) at the time of bone mineral density (BMD) estimation. The majority of women had used one or more contraceptive beside DMPA. The most commonly used alternative contraceptive was the oral combined pill (OCP). It was used by 65% of women (n=143) and for an average duration of 6 years. A logistic regression model was used to estimate the association between potential risk factors and low bone mass.

The prevalence of low bone mass at either hip or spine (T< or =1) was 41%. The prevalence of a T score below -2.5 was 5%, and 45% of women had already sustained one fracture. Younger age was associated with higher BMD [odds ratios (ORs), 0.054; 95% confidence interval (CI), 0.007-0.431]. However, this protective effect of age was lost once the interaction between the duration of both DMPA and OCP was introduced into the model (OR for low BMD, 1.42; 95% CI, 1.09-1.8). The use of DMPA first before ever use of OCP was particularly detrimental to BMD (OR, 3.94; 95% CI, 1.08-14.0). On the contrary, body mass index was positively associated with BMD (OR, 0.86; 95% CI, 0.8-0.9). No other demographic or anamnestic variables significantly predicted the presence of low BMD in this group of young women. This group of DMPA users appear to be at a very high risk of both low BMD and fractures, possibly independently of DMPA use. This needs to be considered when writing guidelines for risk assessment.

The use of DMPA before achievement of peak bone mass may be particularly detrimental to bone, but switching DMPA with the OCP in these women does not seem to confer specific benefit in terms of bone density. This needs to be taken into consideration when a change in contraceptive is considered purely for the sake of bone protection.