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© 1991 Oxford University Press

research-article

A Multicentre Study of Coagulation and Haemostatic Variables during Oral Contraception: Variations with Geographical Location and Ethnicity

I LECK*, J M THOMSON**, J A BOCAZ{dagger}, P BARJA{dagger}, J BONNAR{ddagger}, L DALY{ddagger}, A CARROL{ddagger}, E COUTINHO§, M GONCALVES§, M TSAKOKboxV, S KOHboxV, L POLLER**,, S HOLCK, O AYENI and A PINOL

*Department of Public Health and Epidemiology, University of Manchester Manchester, UK.
**UK Reference Laboratory for Anticoagulant Reagents and Control, Withington Hospital, University Hospital of South Manchester Manchester, M20 8LR, UK.
{dagger}WHO Collaborating Centre for Research in Human Reproduction Santiago, Chile.
{ddagger}Department of Obstetrics and Gynaecology, Trinity College Medical School, St James' and Rotunda Hospitals, University of Dublin Ireland.
§WHO Collaborating Centre for Research in Human Reproduction Salvador, Brazil:
boxVWHO Collaborating Centre for Research in Human Reproduction Singapore.
¶Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization Geneva, Switzerland.

1Reprint requests to: Professor L Poller. UK Reference Laboratory for Anticoagulant Reagents and Control, Withington Hospital, Manchester M20 8LR, UK.

A comparative study of the effects of combined oral contraceptives (OC) on coagulation and fibrinolytic variables using standardized laboratory technique and methodology has been performed in Dublin (Ireland), Salvador (Brazil), Santiago (Chile) and Singapore. Of 777 entrants to the study, 622 were randomly allocated to receive one of four different OC formulations. The remainder did not opt for OC. The progestogenic component was levonorgestrel (LNG) in three of the OC formulations and norethisterone acetate (NEA) in the fourth. Results for the three LNG user groups were pooled. The changes in haematological variables observed over 12 months in the LNG and NEA users were examined in relation to the changes seen in the women not on OC.

Women in Salvador differed markedly from those in the other three centres, in showing no acceleration of the prothrombin time and no increase in either fibrin plate lysis or plasminogen following the use of OC. After adjusting the findings in OC users for those in non-users, significant differences in response between centres were also detected for activated partial thromboplastin time (accelerated only in Dublin and Santiago), factor VII activity (increased mainly in Salvador and Santiago) and fibrinogen (for which the most marked changes were an increase in Dublin and a decrease in Salvador).

This variability between centres in the effects of OC on coagulation and fibrinolysis suggests that OC administration in different populations may not carry equal thrombotic risks.

Revised 1 May 1991


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