CHICAGO – Women with mechanical heart valves who unintentionally become pregnant while on warfarin often expect their obstetricians to recommend pregnancy termination, but that’s not what contemporary practice guidelines advocate.
Neither the latest American College of Chest Physicians guidelines (CHEST 2012;141[2 suppl]: e691S-e736S doi 10.1378/chest.11-2300) nor the European Society of Cardiology guidelines (Eur. Heart J. 2011;32:3147-97) recommend pregnancy termination under those circumstances, Dr. Anthony R. Gregg noted at the annual meeting of the American College of Cardiology.
"Studies show the risk to the fetus is fairly low overall, so there’s no recommendation for pregnancy termination," said Dr. Gregg, professor of obstetrics and gynecology, chief of maternal-fetal medicine, and director of obstetrics at the University of Florida Shands Hospital, Gainesville.
This assertion may come as a surprise to many cardiologists and primary care physicians. After all, every medical student has heard of the fetal warfarin syndrome. But while it affects about 30% of pregnancies with first-trimester warfarin exposure, the degree of severity is highly variable, he explained.
Often a woman doesn’t realize she is pregnant until weeks 6-8 of gestation or even later. The fetus has already been exposed to warfarin. Under those circumstances, the guidelines uniformly recommend that the patient with a mechanical heart valve be switched to low-molecular-weight heparin or unfractionated heparin, then returned to warfarin after 13 weeks’ gestation. She is then maintained on that well-studied oral anticoagulant until week 34, when she should once again be switched to low-molecular-weight heparin or unfractionated heparin as the time of delivery draws closer.
In the case of a planned pregnancy, the recommendation is for a patient with a mechanical valve to be on low-molecular-weight heparin or unfractionated heparin from the time of conception through 13 weeks’ gestation before switching back to warfarin. But that guidance doesn’t apply to women with the older mechanical heart valves posing maximum thromboembolic risk; those patients are best managed on warfarin continuously throughout pregnancy until the week-34 switch to low-molecular-weight heparin or unfractionated heparin.
"We try to point out to patients that they’re not out of the woods despite the fact that we’re following professional organizations’ guidelines. Sometimes they assume that since we’re following guidelines there’s no risk at all. The bottom line is warfarin can cross the placenta in pregnancy. There are lots of documented cases of fetal intracranial bleeding. We follow our patients across pregnancy looking for any evidence of warfarin-induced fetal intracranial hemorrhage," he said.
Dr. Gregg reported having no financial conflicts.