Obstetric thromboprophylaxis is difficult. Since 10 years Swedish obstetricians have used a combined risk estimation model and recommendations concerning to whom, at what dose, when, and for how long thromboprophylaxis is to be administrated based on a weighted risk score. In this paper we describe the background and validation of the Swedish guidelines for obstetric thromboprophylaxis in women with moderate-high risk of VTE, that is, at similar or higher risk as the antepartum risk among women with history of thrombosis. The risk score is based on major risk factors (i.e., 5-fold increased risk of thromboembolism). We present data on the efficacy of the model, the cost-effectiveness, and the lifestyle advice that is given. We believe that the Swedish guidelines for obstetric thromboprophylaxis aid clinicians in providing women at increased risk of VTE with effective and appropriate thromboprophylaxis, thus avoiding both over- and under-treatment. 1. Introduction The incidence of obstetric venous thromboembolism (VTE) in the Nordic countries is estimated at 10 to 13 cases per 10000 pregnancies, half of them diagnosed during the first six weeks after birth [1, 2]. VTE is one of the most common causes of maternal death [3, 4] and leads to morbidity in the form of postthrombotic syndrome in up to 50–60% [5, 6]. Several factors are known to increase the risk of obstetric VTE, such as personal or family history of VTE, thrombophilia, older age, high body mass index (BMI), immobilization, surgery, smoking, nulliparity, and cancer [1, 2]. Thromboprophylaxis during pregnancy usually consists of daily subcutaneous injections of low molecular weight heparin (LMWH), in combination with compression stockings [7–10]. There are several recommendations concerning how to identify women at high risk of VTE during pregnancy and the puerperium. Some of them divide women into low-medium and high-risk groups [7, 8] and others are based on weighted risk scores [9, 10]. Risk assessment and management of obstetric thromboprophylaxis differ in different countries. The aim of this paper is to describe the background and validation of the Swedish guidelines for obstetric thromboprophylaxis in women with moderate-high risk of VTE. A weighted risk score for estimation of obstetric VTE risk has been used in Sweden for around 10 years. Recommendations concerning to whom, at what dose, when, and for how long thromboprophylaxis is to be administered are based on this risk score. A small number of special cases (women with antithrombin deficiency, antiphospholipid syndrome (APS) with
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