Factors that increase the likelihood of deep vein thrombosis (DVT) in pregnancy

Some factors are known to increase susceptibility to this problem. Among the leading factors are:

High parity: The higher the number of deliveries in the past, the higher the risk. It means; all other things being equal, a mother in her fifth pregnancy is at a higher risk of DVT compared to the risk in a first pregnancy.
Obesity: Apart from other problems, an expectant mother who is overweight is at an increased risk of DVT. The increase in risk is roughly in a linear fashion: the higher the weight, the higher the risk.
Immobilization: Prolonged lack of physical activity during pregnancy (which may range from enforced confinement to bed or lounging about in front of the television interminably, to long-haul air travel) are recognized risk factors especially in late pregnancy.
Caucasian race: There is a clear ethnic difference in susceptibility to thrombosis. Women of Asian and black African ancestry are less susceptible when compared to white Caucasian women.
The older mother: Pregnancy in the late thirties and afterwards is associated with increased risk of thrombosis.
Dehydration: Inadequate fluid intake in the face of excessive fluid loss, be it through vomiting, diarrhea, vigorous exercise etc. leads to dehydration. This increases the risk of thrombosis.
Previous history: A pregnant mother with a past history of thrombosis or thrombo-embolism, even if this was not during pregnancy, is at a higher than average risk of thrombosis complicating her pregnancy.

Of course, these factors may not appear in isolation. As such, if a mother in early pregnancy is at a weight of 95 kg (over 200lb), age 38, in her sixth pregnancy and complains of a backache which is confining her to the settee most of the day, even in the absence of a previous history of thrombosis, she is clearly high risk indeed.

Sickle cell disease as a risk factor for thrombosis in pregnancy

The very nature of the condition makes clot formation within the vessels more likely. People suffering from this condition will almost always be aware of the fact that they have to avoid dehydration, which increases the risk of a "sickling" crisis, which in itself may lead to thrombosis. This condition is discussed in greater detail in the section "Thalassemia and sickle cell disease"

Other risk factors for thrombosis in pregnancy

The other two significant risk factors are malignancy and conditions collectively known as "Thrombophilia syndrome".

A malignant disease (cancer) during pregnancy will tend to increase risk of thrombosis.

Lack of physical activity is a recogniszed risk factor for deep vein thrombosis in pregnancy