Oestrogen-progestogen oral contraception and blood clotting: a long-term follow-up.

In a long-term study of women taking the combined oestrogen/progestogen oral contraceptives Ortho-Novin and Norinyl-1 the follow-up has been continued for three years and four years respectively.Acceleration of both "intrinsic" and "extrinsic" clotting tests and of specific factor VII and X assays, reported previously at the nine-month stage, persisted throughout the period of study. Acceleration of Chandler's tube platelet aggregation and hypercoagulable thrombelastographic patterns were recorded. There was, however, no evidence of a cumulative effect after the first nine months.