Warfarin dosage in postpartum women: a case-control study.

Objective: To investigate the clinical suspicion that postpartum women are more difficult to anticoagulate with warfarin than non-pregnant women due to the physiological changes in coagulation proteins that persist into the postpartum period.

Design: A retrospective case-control study.

Setting: University Hospital, Nottingham, UK.

Sample: Twenty-three postpartum women discharged from the obstetric wards on warfarin and 23 age-matched control women discharged from the medical wards on warfarin were identified using hospital databases.

Methods: Warfarin doses and international normalised ratio values were recorded from day one to 35. The number of days and total warfarin dose to achieve therapeutic international normalised ratio were recorded. Doses were compared with those recommended by a dosing nomogram.

Results: The postpartum group took significantly longer and significantly larger doses of warfarin to reach therapeutic international normalised ratio (P < 0.05). The postpartum group required a persistently higher maintenance dose of warfarin. Comparing the warfarin dose given on day three with a standardised nomogram, 79% of women in the postpartum group compared with 57% in the control group were under-dosed.

Conclusion: Postpartum women require larger doses of warfarin to reach therapeutic international normalised ratio than non-pregnant women. We would recommend the use of a dosing nomogram.