Oral Anticoagulants During Pregnancy
Abstract & Commentary
By Michael H. Crawford, MD, Editor
Source: De Santo LS, et al. Mechanical aortic valve replacement in young women planning on pregnancy. J Am Coll Cardiol 2012;59:1110-1115.
Newer bileaflet mechanical heart valves require lower doses of oral anticoagulants to avoid valve thrombosis and embolism genesis. However, little is known about the safety of low-dose regimens in pregnant women who have a hypercoagulable state, yet warfarin embryopathy is known to be dose related. Thus, these investigators from Italy tested women who chose mechanical valve replacement with warfarin anticoagulation before conception was attempted, and then when they became pregnant allowed them three options: 1) the standard heparin in the first trimester, warfarin until the 36th week, and then warfarin until delivery; 2) oral anticoagulation throughout pregnancy until the 36th week, then heparin; or 3) warfarin throughout pregnancy, which was stopped 2 days ahead of planned cesarean delivery and resumed 1 day after delivery. Warfarin was dose adjusted to an INR of 1.5-2.5. Among 20 women with a mechanical aortic valve prostheses, 17 achieved the target INR with < 5 mg/day of warfarin prior to valve replacement. All 17 of these women had normal babies. One patient elected to have low-molecular weight heparin and she had a valve thrombosis in the 11th week. The mother and fetus survived emergency reoperation and she then went on warfarin. The remaining 16 chose option 3 and had no thrombolic or hemorrhage complications. The authors concluded that low-dose oral anticoagulation during pregnancy in women with modern bileaflet aortic valve prostheses is feasible and safe for both the mother and the fetus.
This is an observational study that resulted from a multidisciplinary program in Italy that provided preoperative counseling to women referred for valve surgery who were contemplating pregnancy. Thus, they were able to test preoperatively which women could achieve an INR of 1.5-2.5 on < 5 mg/day of warfarin. This could be achieved in 85% of the women and all but one of them selected a mechanical valve with the continued warfarin/cesarean section option. These 16 women were the study group. One problem with this approach is that the hypercoagulable state of pregnancy may negate the results of the pre-pregnancy warfarin challenge. In fact, the mean dose of warfarin during pregnancy to achieve the target INR was 4 mg/day which was identical to the pre-pregnancy challenge dose. So at least in this pilot study this approached worked.
Of course this was a highly selected population that was monitored weekly and achieved the target INR 80% of the time. Whether this could be applied to less resource intense situations successfully could be challenging. Also, one cannot condemn low-molecular weight heparin during pregnancy based on their one case, but it is consistent with other reports. Another approach could be a bioprosthetic valve and then if it deteriorates later, replace it with a transcutaneous valve. Although provocative, this study does not establish the best way to resolve the dilemma of managing prosthetic valves during pregnancy. However, it may stimulate a longer, more definitive study.