Epidemiology, Risk Factors and Risk Stratification of Venous Thromboembolism in Pregnancy and the Puerperium

Venous thromboembolism (VTE) remains a leading cause of direct maternal deaths in the developed countries. The incidence of VTE has increased significantly during the past two decades. The absolute risk of VTE is estimated 0.6-2.2 per 1000 deliveries. Compared with age-matched non-pregnant women, the daily risk of VTE is increased 7-to 10-fold for antepartum VTE, but it is 15- to 35-fold for postpartum VTE. The incidence of pulmonary embolism (PE) during the first 6 weeks postpartum is nearly 15-fold higher compared to the incidence in pregnancy, and remains significantly increased up to 12 weeks postpartum. The case fatality rate of PE ranges from 2.2 to 6.6%. The basis of VTE prevention is careful assessment of individual risk factors of VTE and proper risk stratification. It is necessary to differentiate preexisting maternal from transient pregnancy-specific risk factors. Women with previous VTE or hereditary high-risk thrombophilias or with the antiphospholipid syndrome have the highest risk for VTE in pregnancy and the puerperium. Other most important pregnancy-specific risk factors in the antenatal period are severe ovarian hyperstimulation syndrome, hyperemesis, major surgery, severe comorbidities (e.g., systemic lupus erythematodes), hospitalization in women with a body mass index >25 kg/m(2), and inflammatory bowel diseases. Heart diseases, stillbirth, systemic infections, severe postpartum hemorrhage in combination with blood product replacement and/or surgery and emergency caesarean section are predominant risk factors in the postpartum period. Recommendations for risk stratification vary among current international guidelines. According to the SOGC (Society of Obstetricians and Gynaecologists of Canada) 2014, pharmacologic VTE prophylaxis is recommended if the estimated absolute risk of one or multiple risk factors is greater than 1%. The ACCP (American College of Chest Physicians) Guideline 2012 presents specific recommendations only for post-caesarean risk-factor-based prophylaxis. The recent RCOG (Royal College of Obstetricians and Gynaecologists) Guideline No. 37a 2015 recommends risk stratification for VTE prophylaxis on the basis of a special risk scoring system weighting individual risk factors between one point (low risk) to a maximum of 4 points (very high risk). A check list of important risk factors and a management plan for thromboprophylaxis based on current guidelines should be readily available in each obstetric unit.