Since we consider we will not have enough patients to detect any significant treatment difference earlier, a mid-term preliminary analysis will be done at 18 months. The objective of this analysis is to evaluate if there is an important difference between the two groups related to disease activity or adverse effects. If there was a satisfactory answer to the main study hypothesis or an unexpectedly higher number of thrombotic events would be present in the hormone therapy group, the study will be finished. As a stopping rule, a two-tailed significance level for SLE activity P < 0.01 has been established, or the presence of >3 thrombotic events in the hormone therapy group. If a P value between 0.01 - 0.05 was detected in the interim analysis, a second analysis will be undertaken 9 months later with an identical stopping rule for both SLE activity and thrombosis.