**4. Interaction of VTE risk factors and potencial risk scores**

The interaction of VTE risk factors remains an important knowledge gap. However in a large hospital- based case–control study, including 559 women with objectively verified VTE during pregnancy or the postpartum period and 1229 controls, some risk factors exhibited additive interaction (as observed with the combination of assisted reproductive technology with multiple pregnancy, and emergency cesarean section with infection), while others appeared to act as multipliers, as with the combination of antepartum immobilization and elevated body mass index [12, 13].

In particular, understanding how these VTE risk factors translate into absolute PA-VTE is essential. A risk prediction model for postpartum VTE was recently developed using large data on 433 353 deliveries. This model was externally validated using another data sets of 662 387 deliveries. Emergency cesarean section, stillbirth, varicose veins, preeclampsia/eclampsia, infection, and medical comorbidities were the strongest VTE predictors in the final multivariable model. The risk prediction model was able to discriminate postpartum women with and without VTE with statistical significance [C statistic of 0.70 (95% CI, 0.67-0.73)] [13].

The risk assessment models in surgical patients (e.g., Caprini and Padua) to predict VTE after cesarean delivery has not been adequately studied suggesting the establishment of a maternal clinical registry and more extensive research to identify optimal models with which to predict VTE risk in the obstetrical population [4, 13].

At the Maternity Hospital of the Hospital das Clínicas, Universidade de São Paulo in Brazil – a tertiary referral service provider for obstetric pathologies - a risk score for VTE was developed since 2014. Since the establishment of this risk score, there have been no more maternal deaths from PE during hospitalization or up to three months postpartum. Among patients who received prophylaxis with enoxaparin, 0.4% had VTE (failure of treatment); in the untreated (that is, low risk) group had 0.06% of VTE. In our institution we have adapted this score since


#### **Table 1.**

*Risk factors for VTE in hospitalization of pregnant women and puerperal women.*

2020 and The National Specialized Commission on Thromboembolism of the Febrasgo (CNE-TEV), based on this national experience proposes the risk score for pregnant women and hospitalized mothers in Brazil. The risk factors were divided into high, medium and low risks, which score, respectively, 3, 2 or 1 point. The fine score occurs by the sum of the values attributed to each factor present in the patient. Pharmacological anticoagulation with is indicated for patients with a score risk of VTE greater than or equal to three [14, 15].

The score is summarized in **Table 1**.

#### **5. Considerations for VTE prophylaxis in cesarean section**

A Cochrane's systematic review concluded that there is insufficient evidence of post-cesarean thromboprophylaxis due to the small number of studies and different comparison criteria. Although the risk of VTE associated with cesarean section is low, when there is a relationship with other risk factors, the occurrence of VTE becomes significant and the institution of thromboprophylaxis should be indicated [1, 2].

Based on observational data, some authors have attempted to calculate the number needed to treat (NNT) to prevent 1 episode of VTE during the postpartum period, and reported that among women deemed at high risk for VTE postpartum, 640 as high as 4000 would require prophylaxis to prevent 1 episode of VTE [13].

The potential benefit of pharmacologic prophylaxis needs to be weighed against the potential for adverse outcomes associated with the intervention. The use of pharmacologic VTE prophylaxis after cesarean delivery has been associated with increased rates of wound morbidity. The number needed to harm (NNH) with the use of pharmacologic VTE prophylaxis after cesarean delivery has been reported to be as low as 200. Due to inadequate sample calculation in the available studies the optimal risk threshold for initiating pharmacological thromboprophylaxis in the antepartum and postpartum periods, particularly in women with lowerrisk thrombophilic traits and multiple (common) VTE risk factors remains to be established [16].

Another question is optimal optimal time to start and duration of thromboembolism prophylaxis after a cesarean delivery. Recent guidelines have addressed the optimal interval between neuraxial anesthesia and initiation of pharmacologic VTE

#### *VTE Prophylaxis in Cesarean Section DOI: http://dx.doi.org/10.5772/intechopen.98974*

prophylaxis to prevent the development of spinal or epidural hematomas take in consideration the time of insert and removal of epidural catheter [5, 15, 16]. Prophylactic doses of enoxaparin (40 mg subcutaneously every day) may be started postoperatively as early as 4 hours after catheter removal but not earlier than 12 hours after the block was performed [4, 15, 17]. Another complication to be considered is iatrogenic postoperative bleeding. The risk of bleeding with prophylactic doses are usually mild, such as wound hematomas, and rarely life-threatening hemorrhagic complications [16–21]. In cases with significant intraoperative bleeding complications, the decision of when to start pharmacologic prophylaxis (if indicated) must be individualized according with the clinical and surgical scenarios [2, 3, 21].

Although the evidence is scarce Women with risk factors should receive thromboprophylaxis at minimum for 6 weeks postpartum; women with transient risk factors in the antepartum and intrapartum should receive thromboprophylaxis until hospital discharge or up to 2 weeks after delivery [2–5].

In SARS COVID-19 given the potential increase in VTE risk a weight-adjusted VTE prophylaxis with low molecular weight heparin (LMWH) should be considered in all pregnant and post partum women admitted to hospital (in the absence of active bleeding and with a platelet count above 30 × 109/L or indication for immediate delivery). In case of indicated or emergency delivery VTE prophylaxis should be evaluated individually [10, 11].
