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Effects of Low-dose Oral Contraceptives on Blood Coagulation

Br Med J 1968; 3 doi: (Published 27 July 1968) Cite this as: Br Med J 1968;3:218
  1. L. Poller,
  2. Anne Tabiowo,
  3. Jean M. Thomson


    A study has been performed on the effect of Norinyl-1 and Ortho-Novin, two low-dose oral contraceptives, on blood-clotting factors. Ortho-Novin contains twice the amount of hormone as Norinyl-1. It was therefore possible to observe whether any changes detected were related to the dose of oestrogen-progestin combination. The women were tested in parallel with matched normal female controls and a group in the third trimester of pregnancy. Significant rises in factor VII and X levels were found with both low-dose preparations from the third month onwards. There was no difference between patients on Norinyl-1 and Ortho-Novin, and hence the clotting changes do not appear to be dose-dependent. The long-term effects on clotting factors of these low-dose oral contraceptive preparations remain to be investigated.


    • * This work was undertaken with the financial assistance of a grant for thrombosis research from Manchester Regional Hospital Board and a grant from the Council for the Investigation of Fertility Control. Syntex Pharmaceuticals Ltd. kindly provided the low-dose hormone preparation used in this study and patient data sheets.