Pregnancy, Clotting, and Factor V Leiden: An Overview
The past 10 years have brought new understanding of and explanations why
some women clot on birth control pills and during pregnancy. Research into
genetic origins of disease has uncovered many coagulopathies, some of them
surprisingly common. The most common is Factor V Leiden, also known as
Activated Protein C Resistance, which carries a 3-10 times greater risk of
clot when someone has one copy of the gene and 30-140 times greater risk of
clotting for someone with two copies.

Between 3% and 10% of Caucasian people are heterozygous for Factor V
Leiden, and a much smaller percentage are homozygous. In Sweden the rate of
heterozygous mutation may be as high as 15% in some areas, while in other
parts of the world and among other races only a fraction of a percent of
the population may have it. It is thought that the original mutation
occurred as much as 20,000-30,000 years ago in a single individual.(1)

Women with Factor V Leiden (FVL) have a substantially increased risk of
clotting in pregnancy (and on estrogen containing birth control pills or
hormone replacement) in the form of DVT (deep vein thrombosis, sometimes
known as "milk leg") and pulmonary embolism. They also have an increased
risk of preeclampsia, as well as miscarriage and stillbirth due to clotting
in the placenta, umbilical cord, or the fetus (fetal clotting may depend on
whether the baby has inherited the gene). Note that many, many of these
women go through one or more pregnancies with no difficulties, while others
may miscarry over and over again, and still others may develop clots within
weeks of becoming pregnant.

There may be nutritional and lifestyle reasons why some women clot and some
women don't. There is some evidence that low magnesium levels can increase
the tendency to clot (2). Likewise, high homocysteine levels may magnify
the effects of FVL or vice versa. The treatment for high homocysteine
levels is supplementation of vitamins B-6, B-12, and folic acid (3). Both
birth control pills and pregnancy demand higher intake of these nutrients,
so nutritional deficiencies in women with FVL can have extreme
consequences. Likewise, women who exercise regularly and are not immobile
for long periods of time will have better circulation and less opportunity
for clots to form. Given that the vast majority of people with FVL are
unaware of the condition, and the fact that in the U.S. it is a safe bet
that every midwife has had at least one and probably many clients with FVL,
it pays to be aware both of the nutritional issues and the symptoms of
abnormal clotting.

Women who are diagnosed with FVL are generally considered high risk in
pregnancy, particularly if they have had clotting in the past. Standard
medical practice in most cases is prophylactic treatment with low-dose Low
Molecular Weight Heparin (LMWH, usually Lovenox) for women who are not
actively clotting and therapeutic anticoagulation with LMWH for women with
active clotting. There is considerable debate about appropriate treatment
for women who are diagnosed (due to having relatives with problems) who
have not had any clotting episodes. It may be that these women do not need
to be anticoagulated with heparin, and may instead simply follow a regimen
of careful nutrition and a baby aspirin per day, if that.

Some herbs may be useful if women with FVL choose not to use heparin.
Garlic, ginger, ginkgo and purple grape juice are just a few of the many
foods and herbs with anticoagulant activity.

Remember that approximately one in twenty of the women you serve will have
FVL. Approximately one in a hundred of women with FVL (estimates vary
radically from a 1% thrombosis rate (4) to a 25% thrombosis rate (my
hemotologist) will have a serious DVT during pregnancy. Please be aware of
warning signs of deep vein thrombosis (tenderness, swelling, pain that does
not subside) and pulmonary embolism (shortness of breath with pain,
localized pain that does not subside, a 'bruised' feeling on deep inhale).
Both are easily confused with other problems but can be life threatening.
Most people are initially misdiagnosed. Listen to your mothers!

1) Zivelin, A, Rosenberg, N, et al. (1998). A single genetic origin for the
common prothrombotic G20210A polymorphism in the prothrombin gene. Blood,
A discussion of the merits of screening for Factor V Leiden in oral
contraceptives users. Gives detailed descriptions of testing methods and
reasons why screening may or may not be useful.
"Estimates suggest that there are 5 cases of venous thrombosis per 100,000
women not using oral contraceptives per annum, 15 per 100,000 women users
of second generation oral contraceptives and 30 per 100,000 users of third
generation oral contraceptives, and 60 per 100,000 pregnancies." This
superb article describes very realistically the shortcomings of testing.
Describes some of the differences in risk factors for clotting.
Gives a rundown on risk factors. The second page gives testing and
treatment options.

Other resources: has information and a mailing list. is an egroups mailing list for
pregnancy and FVL.

by Jennifer Rosenberg
Jennifer Rosenberg has been trained as a doula and childbirth educator. She currently works as a graphic designer, editor and author for Midwifery Today, Inc.

Reprinted from Midwifery Today E-News (Vol 2 Issue 19 May 12, 2000)
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