**13. Pregnancy**

Pregnancy-associated DVT based on data from the National Hospital Discharge Survey was diagnosed in 93,000 of 80,798,000 women (0.12%) from 1979 to 1999.151 The rate of pregnancyassociated DVT (vaginal delivery and cesarean section) increased from 1982 to 1999, although the rate of nonpregnancy-associated DVT decreased for most of this period. Some showed the rate of pregnancy-associated DVT was twice the rate of nonpregnancyassociated DVT.159 A 6-fold increase in the rate of thromboembolism during pregnancy and the puerperium compared with nonpregnant women has been reported by others.160 Although the rate of pregnancy-associated DVT was higher than the rate of nonpregnancyassociated DVT, the rate of pregnancyassociated PE was lower than

Pathophysiology of venous thromboembolism during Pregnancy:

Increased venous distensibility and capacity, with a resultant reduction in the velocity of blood flow in the lower limbs, are demonstrable from the first trimester of pregnancy162,163. These changes are compounded by a 20–25% increase in the overall circulatory volume during pregnancy164. Obstruction of the inferior vena cava by the enlarging gravid uterus may also result in increased stasis165. Compression of the left iliac vein by the right iliac artery as they cross 166 may explain the preponderance of left leg DVT during pregnancy 161,167.

Altered levels of coagulation factors have been described both during pregnancy and postpartum. Hypercoagulability is thought to be promoted by increases in coagulation factors such as fibrinogen, von Willebrand factor, and factor VIII:C 168,169–171, as well as by decreases in natural inhibitors of coagulation such as protein S 172 and the development of an acquired resistance to the endogenous anticoagulant, activated protein C 173. In addition, a reduction in global fibrinolytic activity has been described during pregnancy 174, perhaps as a consequence of increases in the levels of plasminogen activator inhibitor 1 (PAI 1) and plasminogen activator inhibitor 2 (PAI 2) 174–176, the latter being produced by the placenta.

Exogenous risk factors also appear to determine the thrombotic risk associated with pregnancy. In a retrospective cohort study of unselected consecutive patients with confirmed pregnancy-related venous thromboembolism, approximately two-thirds of patients had an identifiable acquired risk factor (for example, age over 35 years, intercurrent illness, immobility, increased parity or caesarean section) 177.

The reason for this difference is unknown and could reflect difference of the natural history of DVT in pregnancy. It also could reflect a reluctance to expose pregnant women to ionizing radiation associated with imaging for PE, resulting in a decreased frequency of diagnosis of PE. The rate of pregnancy-associated DVT was higher among women aged 35 to 44 years than in younger women. The rate of pregnancyassociated DVT among black

carcinoma of the pancreas (4.3%) and the lowest incidences were in patients with carcinoma of the bladder and carcinoma of the lip, oral cavity, or pharynx (<0.6% to 1.0%). Incidences with cancer were not age dependent.157 Myeloproliferative diseaseand lymphoma were associated with relative risks for VTE of 2.9 and 2.5, respectively157 Leukemia was associated with a lower relative risk (1.7). Based on death certificates from 1980 to 1998 among patients who died with cancer, PE was the listed cause of death in 0.21%.158 Adjustment of the data for the frailty of the diagnosis of fatal PE based on death certificates

Pregnancy-associated DVT based on data from the National Hospital Discharge Survey was diagnosed in 93,000 of 80,798,000 women (0.12%) from 1979 to 1999.151 The rate of pregnancyassociated DVT (vaginal delivery and cesarean section) increased from 1982 to 1999, although the rate of nonpregnancy-associated DVT decreased for most of this period. Some showed the rate of pregnancy-associated DVT was twice the rate of nonpregnancyassociated DVT.159 A 6-fold increase in the rate of thromboembolism during pregnancy and the puerperium compared with nonpregnant women has been reported by others.160 Although the rate of pregnancy-associated DVT was higher than the rate of

Increased venous distensibility and capacity, with a resultant reduction in the velocity of blood flow in the lower limbs, are demonstrable from the first trimester of pregnancy162,163. These changes are compounded by a 20–25% increase in the overall circulatory volume during pregnancy164. Obstruction of the inferior vena cava by the enlarging gravid uterus may also result in increased stasis165. Compression of the left iliac vein by the right iliac artery as they

Altered levels of coagulation factors have been described both during pregnancy and postpartum. Hypercoagulability is thought to be promoted by increases in coagulation factors such as fibrinogen, von Willebrand factor, and factor VIII:C 168,169–171, as well as by decreases in natural inhibitors of coagulation such as protein S 172 and the development of an acquired resistance to the endogenous anticoagulant, activated protein C 173. In addition, a reduction in global fibrinolytic activity has been described during pregnancy 174, perhaps as a consequence of increases in the levels of plasminogen activator inhibitor 1 (PAI 1) and plasminogen activator inhibitor 2 (PAI 2) 174–176, the latter being produced by the placenta. Exogenous risk factors also appear to determine the thrombotic risk associated with pregnancy. In a retrospective cohort study of unselected consecutive patients with confirmed pregnancy-related venous thromboembolism, approximately two-thirds of patients had an identifiable acquired risk factor (for example, age over 35 years, intercurrent

The reason for this difference is unknown and could reflect difference of the natural history of DVT in pregnancy. It also could reflect a reluctance to expose pregnant women to ionizing radiation associated with imaging for PE, resulting in a decreased frequency of diagnosis of PE. The rate of pregnancy-associated DVT was higher among women aged 35 to 44 years than in younger women. The rate of pregnancyassociated DVT among black

nonpregnancyassociated DVT, the rate of pregnancyassociated PE was lower than

cross 166 may explain the preponderance of left leg DVT during pregnancy 161,167.

Pathophysiology of venous thromboembolism during Pregnancy:

illness, immobility, increased parity or caesarean section) 177.

indicated a likely range of 0.31% to 1.97%.158

**13. Pregnancy** 

women was higher than among white women.159,178,179 DVT was more frequent among women who underwent cesarean section (104/100,000/y) than those who underwent vaginal delivery (47/ 100,000/y).159 VTE in pregnancy is discussed in detail in the article by Marik elsewhere in this issue.
