Assessment of VTE risk in pregnancy

Pregnancy and the postpartum period are risk factors for the development of venous thromboembolism (VTE) (ie deep vein thrombosis [DVT] or pulmonary embolism [PE]), which is an important cause of maternal morbidity and mortality. Although the risk of VTE in pregnancy is 4- to 5-times greater than the risk in nonpregnant patients, the absolute risk is low (incidence of VTE of 1 or 2 per 1000 pregnancies)McLintock, 2012.

Assess patients for the risk of VTE in early pregnancy or prepregnancy. A table of VTE risk factors in pregnancy and the immediate postpartum period (puerperium) can be found in the Royal College of Obstetricians and Gynaecologists (RCOG) Green-top Guideline No. 37a. The New South Wales Clinical Excellence Commission also provide a maternity risk assessment tool.

If prophylaxis is not required on initial assessment, continue to observe patients for possible signs and symptoms of VTE throughout pregnancy and the postpartum period. Also reassess pregnant patients if they develop complications during pregnancy and are admitted to hospital; they may require VTE prophylaxis while in hospital.

Limited evidence suggests that risk factors for VTE are synergistic. Only patients with additional risk factors for VTE (other than pregnancy) require prophylaxis. While some risk factors are particular to pregnancy (eg multiparity, multiple pregnancy, pre-eclampsia, caesarean section), risk factors applicable to the general population also apply (see Risk factors for VTE in nonsurgical patients in hospital).

The most common risk factors that warrant VTE prophylaxis for pregnant patients are:

  • a history of prior hormone-associated VTE
  • a history of prior unprovoked VTE
  • the presence of high-risk hereditary thrombophilia (eg homozygous factor V Leiden gene mutation), whether there is a history of VTE or not.

The need for primary prophylaxis in pregnant patients with hereditary thrombophilias differs between guidelines; see Table 3 in the American Society of Hematology 2018 guidelines for management of VTE in pregnancy. The presence of antiphospholipid antibodies may increase the risk of both maternal VTE and fetal death—see Antiphospholipid syndrome.