Effects of low-dose oral contraceptives on blood coagulation.

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.