Venous thromboembolism is a condition that causes formation of blood clots in the body. It may have life threatening consequences if the leg veins, lungs or the brain blood vessels are involved. In pregnancy, a woman's baseline risk for forming blood clots is increased.

Women with a known prior blood clot during pregnancy, artificial heart valves or other genetic conditions are at a very high risk for these complications during their pregnancy. It has been well established that these women benefit from medical treatment with a blood thinning medication in their pregnancies to prevent further formation of blood clots. These medications are called Heparins and are given as shots. Prior studies have suggested that a type of Heparin called "low molecular weight heparin" (Enoxaparin=Lovenox®) is well suited for use in pregnancy as it does not affect the baby and has a very low complication rate. The standard dose given for treatment of these patients has been established previously. However, there is a concern that complications may occur if the concentration of this medication falls below its effective level. It is of particular importance in pregnancy, as the rate of breakdown of this medication increases in pregnancy and may lead to lowering of its effective levels.

Our study will evaluate the blood levels of enoxaparin before and after administration of this medication in pregnant women who are receiving this drug for treatment. This will determine whether an increase in the dose or an increase in the frequency of dosing might further improve the standard of care.