Physiologic Changes During Pregnancy and Impact on Small-Molecule Drugs, Biologic (Monoclonal Antibody) Disposition, and Response

Pregnancy is a unique physiological state that results in many changes in bodily function, including cellular, metabolic, and hormonal changes. These changes can have a significant impact on the way small-molecule drugs and monoclonal antibodies (biologics) function and are metabolized, including efficacy, safety, potency, and adverse effects. In this article, we review the various physiologic changes that occur during pregnancy and their effects on drug and biologic metabolism, including changes in the coagulation, gastrointestinal, renal, endocrine, hepatic, respiratory, and cardiovascular systems. Additionally, we discuss how these changes can affect the processes of drug and biologic absorption, distribution, metabolism, and elimination (pharmacokinetics), and how drugs and biologics interact with biological systems, including mechanisms of drug action and effect (pharmacodynamics) during pregnancy, as well as the potential for drug-induced toxicity and adverse effects in the mother and developing fetus. The article also examines the implications of these changes for the use of drugs and biologics during pregnancy, including consequences of suboptimal plasma drug concentrations, effect of pregnancy on the pharmacokinetics and pharmacodynamics of biologics, and the need for careful monitoring and individualized drug dosing. Overall, this article aims to provide a comprehensive understanding of the physiologic changes during pregnancy and their effects on drug and biologic metabolism to improve the safe and effective use of drugs.

Venous thromboembolism during pregnancy and postpartum period

Venous thromboembolism (VTE) is one of the leading causes of maternal mortality. Rates of VTE during pregnancy and the postpartum period have not decreased over the past two decades and pregnancyassociated VTE continues to pose a significant health challenge. Pregnant and postpartum women are at a higher risk for VTE owing to many factors. There are hormonally mediated and pregnancy-specific alterations of coagulation that favor thrombosis, including increased production of clotting factors. There are physiologic and anatomic mechanisms that also contribute, including a decreased rate of venous blood flow from the lower extemities as pregnancy progresses. Cesarean delivery also introduces VTE risk. In addition, studies have demonstrated that pregnancy-associated complications such as pre-eclampsia or peri-partum infections are associated with increased VTE rates. In this review, we discuss the recent epidemiological studies, pathogenesis, risk factors and clinical presentation as well as therapeutic options for VTE during pregnancy and the postpartum period. We also provide proposed diagnostic algorithms for diagnosis and management of VTE during pregnancy and the postpartum period based on updated evidence. Finally, we highlight knowledge gaps to guide future research.

Comparison of doses of heparin for venous thromboembolism and bleeding in pregnant women

The evaluation criteria for dosage of low-molecular-weight heparin (LMWH) for pregnant women at high risk of venous thromboembolism (VTE) remain unclear. A retrospective study was performed to investigate the relative appropriate LMWH administration strategy and dosage for pregnant women at risk of VTE. 219 pregnant women with perinatal and postpartum VTE were reviewed and divided into group A (fixed dose group: n=73, 5000 IU dalteparin daily for all women), group B (weight group: n=73, 2500 IU dalteparin daily for women less than 50 kg; 5000 IU dalteparin daily for women more than 50 kg), and group C (anti-factor Xa (FXa) + weight group: n=73, 5000 IU once daily for women less than 50 kg; 7500 IU once daily for women weighing 50-80 kg; 10,000 IU once daily for women weighing over 80 kg). Further dose administration was adjusted according to peak anti-FXa level, maintaining the peak at the 0.5-1.0 IU/mL range. Women in group C presented lower incidence of VTE and other pregnancy complications than group A and group B. Adjusting the dosage of LMWH according to both weight and anti-FXa level of pregnant women not only prevented VTE but also reduced the risk of postpartum hemorrhage induced by LMWH administration. In addition, adjusting the dose of LMWH according to anti-FXa level and body weight also affected the recurrence of VTE and the occurrence of postpartum hemorrhage in pregnant women.

Prevention and management of venous thromboembolism in pregnancy: cutting through the practice variation

There is clinical practice variation in the area of prevention and management of venous thromboembolism (VTE) in pregnancy. There are limited data and differing recommendations across major clinical practice guidelines, especially relating to the role of postpartum low-molecular-weight heparin (LMWH) for patients with mild inherited thrombophilia and those with pregnancy-related VTE risk factors. This chapter explores the issues of practice variation and related data for postpartum VTE prevention. Controversial topics of VTE management in pregnancy are also reviewed and include LMWH dosing and the role of anti-Xa level monitoring, as well as peripartum anticoagulation management around labor and delivery.

Anti-Xa Monitoring of Low-Molecular-Weight Heparin during Pregnancy: A Systematic Review

Low-molecular-weight heparin (LMWH) is commonly used for preventing or treating venous thromboembolic disease (VTE) during pregnancy. The physiological changes in maternal metabolism have led to discussions on optimal LMWH dosing strategy and possible need for monitoring. The aim of this systematic review is to summarize and discuss whether LMWH dose adjustment according to anti-Xa provides superior effectiveness and safety compared with weight adjusted or fixed dosed LMWH in pregnant women. A systematic literature search was performed in PubMed, Embase, and Scopus on September 26, 2020. The study is reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Effectiveness was defined as episodes of thrombosis and safety as bleeding episodes. In total, 33 studies were included: 4 randomized controlled studies and 29 cohort studies. Prophylactic dosing strategies employing weight dosed, fixed dosed, or anti-Xa adjusted LMWH dosing performed equal in effectiveness and safety. In pregnant women with VTE or high thromboembolic risk, therapeutic weight-adjusted LMWH and weight plus anti-Xa-adjusted LMWH provided equal results in terms of effectiveness and safety. Pregnant women with mechanical heart valves (MHVs) received therapeutic anti-Xa-adjusted LMWH with four out of seven studies presenting mean peak anti-Xa within target ranges. Still, pregnant women with MHV experienced both thrombosis and bleeding with anti-Xa in target. Based on the results of this systematic review, current evidence does not support the need for anti-Xa monitoring when using LMWH as thromboprophylaxis or treatment during pregnancy. Nonetheless, the need for anti-Xa monitoring in pregnant women with MHV may need further scrutiny.

Pulmonary Embolism in Pregnancy

Even though venous thromboembolism is a leading cause of maternal mortality in high-income countries, there are limited high-quality data to assist clinicians with the management of pulmonary embolism in this patient population. Diagnosis, prevention, and treatment of pregnancy-associated pulmonary embolism are complicated by the need to consider fetal, as well as maternal, well-being. Recent studies suggest that clinical prediction rules and D-dimer testing can reduce the need for diagnostic imaging in a subset of patients. Low-molecular-weight heparin is the preferred anticoagulant for both prophylaxis and treatment in this setting. Direct oral anticoagulants are contraindicated during pregnancy and in breastfeeding women. Thrombolysis or embolectomy should be considered for pregnant women with pulmonary embolism complicated by hemodynamic instability. Treatment of pregnancy-associated pulmonary embolism should be continued for at least 3 months, including 6 weeks postpartum. Management of anticoagulants at the time of delivery should involve a multidisciplinary individualized approach that uses shared decision making to take patient and caregiver values and preferences into account.

American Society of Hematology 2018 guidelines for management of venous thromboembolism: venous thromboembolism in the context of pregnancy

BACKGROUND

Venous thromboembolism (VTE) complicates ∼1.2 of every 1000 deliveries. Despite these low absolute risks, pregnancy-associated VTE is a leading cause of maternal morbidity and mortality.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians and others in decisions about the prevention and management of pregnancy-associated VTE.

METHODS

ASH formed a multidisciplinary guideline panel balanced to minimize potential bias from conflicts of interest. The McMaster University GRADE Centre supported the guideline development process, including updating or performing systematic evidence reviews. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess evidence and make recommendations.

RESULTS

The panel agreed on 31 recommendations related to the treatment of VTE and superficial vein thrombosis, diagnosis of VTE, and thrombosis prophylaxis.

CONCLUSIONS

There was a strong recommendation for low-molecular-weight heparin (LWMH) over unfractionated heparin for acute VTE. Most recommendations were conditional, including those for either twice-per-day or once-per-day LMWH dosing for the treatment of acute VTE and initial outpatient therapy over hospital admission with low-risk acute VTE, as well as against routine anti-factor Xa (FXa) monitoring to guide dosing with LMWH for VTE treatment. There was a strong recommendation (low certainty in evidence) for antepartum anticoagulant prophylaxis with a history of unprovoked or hormonally associated VTE and a conditional recommendation against antepartum anticoagulant prophylaxis with prior VTE associated with a resolved nonhormonal provoking risk factor.

Obstetric venous thromboembolism: a systematic review of dalteparin and pregnancy

A systematic review of studies published between 1 January 1985 and 31 August 2017 was performed to analyse the efficacy of the low-molecular-weight heparin, dalteparin, in venous thromboembolism (VTE) treatment and prophylaxis during pregnancy, and to evaluate dosing practices, anticoagulant monitoring and adverse events. A therapeutic dosing throughout pregnancy or followed by reduced doses effectively prevented VTE recurrence. Anti-factor Xa activity was the most commonly used method of dose monitoring. The risk of bleeding with dalteparin was generally minor. Major bleeding was observed when a high dose of dalteparin was employed during (or close to) delivery, or postpartum. Other adverse events were minor. Disparity exists in VTE treatment and thromboprophylaxis, with wide variety in the dosing regimens, treatment strategies and monitoring practices employed. Large randomised controlled trials are warranted but due to ethical reasons, and the rarity of VTE-associated obstetric complications, case-control, registry and large observational studies present more likely options.

Guidance for the treatment and prevention of obstetric-associated venous thromboembolism

Venous thromboembolism (VTE), which may manifest as pulmonary embolism (PE) or deep vein thrombosis (DVT), is a serious and potentially fatal condition. Treatment and prevention of obstetric-related VTE is complicated by the need to consider fetal, as well as maternal, wellbeing when making management decisions. Although absolute VTE rates in this population are low, obstetric-associated VTE is an important cause of maternal morbidity and mortality. This manuscript, initiated by the Anticoagulation Forum, provides practical clinical guidance on the prevention and treatment of obstetric-associated VTE based on existing guidelines and consensus expert opinion based on available literature where guidelines are lacking.

Pregnancy-Related Venous Thromboembolism

Pregnancy is associated with an increased risk of venous thromboembolism (VTE), with a reported incidence ranging from 0.49 to 2 events per 1000 deliveries. Risk factors include advanced maternal age, obesity, smoking, and cesarian section. Women with a history of previous VTE are at a 4-fold higher risk of recurrent thromboembolic events during subsequent pregnancies. Additionally, the presence of concomitant thrombophilia, particularly factor V Leiden (homozygosity), prothrombin gene mutation (homozygosity), or antiphospholipid syndrome (APS), increases the risk of pregnancy-related VTE. Low-molecular-weight heparin (LMWH) and unfractionated heparin (UFH) are the drugs of choice for anticoagulation during pregnancy. LMWH is preferred due to ease of use and lower rates of adverse events. Women with high thromboembolic risk particularly those with a family history of VTE should receive antepartum thromboprophylaxis. Women with low thromboembolic risk or previous VTE caused by a transient risk factor (ie, provoked), who have no family history of VTE, may undergo antepartum surveillance. Postpartum anticoagulation can be considered in women with both high and low thromboembolic risk.

Population Pharmacokinetics of Enoxaparin During the Antenatal Period

Background—

The optimal dosing strategy of low-molecular-weight heparins for the treatment of antenatal venous thromboembolism is not known. The physiological changes associated with pregnancy alter the pharmacokinetic profile of low-molecular-weight heparins, which has led to controversy and subsequent variation in practice, when pregnant women with venous thromboembolism are treated with low-molecular-weight heparins. Our objective was to develop a robust pharmacokinetic model of enoxaparin during the antenatal period to address this problem.

Method and Results—

Women prescribed antenatal enoxaparin were eligible to enroll in the study. Recruited women were reviewed monthly and had up to 3 anti-Xa activities (trough and 1 and 3 hours after dose) drawn at each clinic attendance. Compartmental pharmacokinetic modeling was conducted using nonlinear mixed-effects modeling. One hundred twenty-three patients contributed 795 anti-Xa activities for pharmacokinetic modeling purposes. Both enoxaparin clearance and volume of distribution were increased during pregnancy. Simulations of once- versus twice-daily enoxaparin administration demonstrated that both dosing regimens would reach target 3-hour plasma concentrations throughout the duration of the pregnancy. When trough anti-Xa activity was simulated, both once- and twice-daily regimens exhibited an increase in trough anti-Xa activity with the progression of pregnancy. This is explained by the significant increase in volume of distribution observed during pregnancy.

Conclusions—

The half-life of enoxaparin is prolonged with the progression of pregnancy, and our work provides compelling evidence for prescribing once-daily enoxaparin for the treatment of antenatal venous thromboembolism. National and international guideline recommendations should be reconsidered.

Anticoagulant therapy for venous thromboembolism during pregnancy: a systematic review and a meta-analysis of the literature

Venous thromboembolism (VTE) is one of the most relevant causes of maternal death in industrialized countries. Low molecular weight heparin (LMWH), continued throughout the entire pregnancy and puerperium, is currently the preferred treatment for patients with acute VTE occurring during pregnancy. However, information on the efficacy and safety of anticoagulant drugs in this setting is extremely limited. We carried out a systematic review and a meta-analysis of the literature to provide an estimate of the risk of bleeding complications and VTE recurrence in patients with acute VTE during pregnancy treated with antithrombotic therapy. The weight mean incidence (WMI) of bleeding and thromboembolic events and the corresponding 95% confidence interval (CI) were calculated. Eighteen studies, giving a total of 981 pregnant patients with acute VTE, were included. LMWH was prescribed to 822 patients; the remainder were treated with unfractionated heparin. Anticoagulant therapy was associated with WMIs of major bleeding of 1.41% (95% CI 0.60-2.41%; I) antenatally and 1.90% (95% CI 0.80-3.60%) during the first 24 h after delivery. The estimated WMI of recurrent VTE during pregnancy was 1.97% (95% CI 0.88-3.49%; I(2) 39.5%). Anticoagulant therapy appears to be safe and effective for the treatment of pregnancy-related VTE, but the optimal dosing regimens remain uncertain.

Venous thromboembolism associated with pregnancy and hormonal therapy

Venous thromboembolism (VTE) is a major cause of maternal morbidity and mortality during or early after pregnancy and in women taking hormonal therapy for contraception or for replacement therapy. Post-thrombotic syndrome, including leg oedema and leg pain, is an unrecognized burden after pregnancy-related VTE, which will affect more than two of five women. Women with a prior VTE, a family history of VTE, certain clinical risk factors and thrombophilia are at considerably increased risk both for pregnancy-related VTE and for VTE on hormonal therapy. This review critically assesses the epidemiology and risk factors for pregnancy-related VTE and current guidelines for prophylaxis and treatment. We also provide information on the risk of VTE related to hormonal contraception and replacement therapy.

The risk of postpartum hemorrhage in women using high dose of low-molecular-weight heparins during pregnancy

BACKGROUND

Low-molecular-weight heparins (LMWH) are the most commonly used anticoagulant during pregnancy for prevention or treatment of VTE. However, the size of the associated risk of postpartum haemorrhage (PPH) is unknown.

OBJECTIVE

To assess the bleeding risk of high dose LMWH, also in relation to time between last dose LMWH and delivery.

MATERIAL AND METHODS

From 1999 to 2009, we followed 88 pregnant women who were started on therapeutic anticoagulation. Controls were pregnant women without LMWH, matched 1:4 for parity, mode of delivery, age, gestational age and delivery date. PPH was defined as >500 ml blood loss for vaginal delivery (severe PPH in vaginal delivery as >1000 ml) and >1000 ml for cesarean section (CS). Women were divided into subgroups by the interval between last dose of anticoagulation and delivery (<12, 12-24 hrs, >24 hrs).

RESULTS

Risk of PPH after vaginal delivery was 30% and 18% for LMWH-users and non-users, respectively (OR 1.9, 95%CI 1.1-3.5). Risk of severe PPH after vaginal delivery was not different (5.6 vs 5.0%; OR 1.1; 0.4-3.6). Risk of PPH after CS was 12% in LMWH-users and 4% in non-users (OR 2.9; 0.5-19.4). Both events of LMWH-users occurred after emergency CS. The risk of PPH associated with delivery within 24 hours after last dose of LMWH was 1.2 fold higher (95%CI 0.4-3.6) compared to a larger interval.

CONCLUSION

High dose LMWH carries an increased risk of more than 500 mL blood loss after vaginal delivery. However, this results not in more clinical relevant severe PPHs. The interval between last dose of LMWH and delivery does not influence the risk of PPH.

Pregnancy-associated venous thromboembolism: prevention and treatment

Pregnancy is associated with an increased risk of venous thromboembolism (VTE) and this condition remains an important cause of maternal morbidity and mortality. The use of anticoagulant therapy for treatment and prophylaxis of VTE during pregnancy is challenging because of the potential for fetal, as well as maternal, complications. Although evidence-based recommendations for the use of anticoagulants have been published, given the paucity of available data, guidelines are based largely upon observational studies and from data in nonpregnant patients. This article reviews the available literature and provides guidance for the management and prevention of VTE during pregnancy.

VTE, thrombophilia, antithrombotic therapy, and pregnancy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The use of anticoagulant therapy during pregnancy is challenging because of the potential for both fetal and maternal complications. This guideline focuses on the management of VTE and thrombophilia as well as the use of antithrombotic agents during pregnancy.

METHODS

The methods of this guideline follow the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

We recommend low-molecular-weight heparin for the prevention and treatment of VTE in pregnant women instead of unfractionated heparin (Grade 1B). For pregnant women with acute VTE, we suggest that anticoagulants be continued for at least 6 weeks postpartum (for a minimum duration of therapy of 3 months) compared with shorter durations of treatment (Grade 2C). For women who fulfill the laboratory criteria for antiphospholipid antibody (APLA) syndrome and meet the clinical APLA criteria based on a history of three or more pregnancy losses, we recommend antepartum administration of prophylactic or intermediate-dose unfractionated heparin or prophylactic low-molecular-weight heparin combined with low-dose aspirin (75-100 mg/d) over no treatment (Grade 1B). For women with inherited thrombophilia and a history of pregnancy complications, we suggest not to use antithrombotic prophylaxis (Grade 2C). For women with two or more miscarriages but without APLA or thrombophilia, we recommend against antithrombotic prophylaxis (Grade 1B).

CONCLUSIONS

Most recommendations in this guideline are based on observational studies and extrapolation from other populations. There is an urgent need for appropriately designed studies in this population.

How I treat pregnancy-related venous thromboembolism

Venous thromboembolism (VTE) complicates ∼ 1 to 2 of 1000 pregnancies, with pulmonary embolism being a leading cause of maternal mortality and deep vein thrombosis an important cause of maternal morbidity, also on the long term. However, a strong evidence base for the management of pregnancy-related VTE is missing. Management is not standardized between physicians, centers, and countries. The management of pregnancy-related VTE is based on extrapolation from the nonpregnant population, and clinical trial data for the optimal treatment are not available. Low-molecular-weight heparin (LMWH) in therapeutic doses is the treatment of choice during pregnancy, and anticoagulation (LMWH or vitamin K antagonists postpartum) should be continued until 6 weeks after delivery with a minimum total duration of 3 months. Use of LMWH or vitamin K antagonists does not preclude breastfeeding. Whether dosing should be based on weight or anti-Xa levels is unknown, and practices differ between centers. Management of delivery, including the type of anesthesia if deemed necessary, requires a multidisciplinary approach, and several options are possible, depending on local preferences and patient-specific conditions.

Dosing and monitoring of low-molecular-weight heparin in high-risk pregnancy: single-center experience

STUDY OBJECTIVE

To evaluate dosing requirements and monitoring patterns of low-molecular-weight heparin (LMWH) when used in high-risk pregnancy.

DESIGN

Retrospective, observational, cohort study.

SETTING

University-affiliated medical center.

PATIENTS

Forty-nine women treated with LMWH between 2001 and 2005 for either prophylaxis or treatment of venous thromboembolism during pregnancy and monitored with antifactor Xa activity.

MEASUREMENTS AND MAIN RESULTS

Data were obtained on 53 pregnancies in the 49 women. The primary outcome was change in dosing requirements of LMWH throughout pregnancy as determined by the corresponding antifactor Xa activity peak levels. Mean starting doses of twice-daily enoxaparin and doses most proximate to delivery were 39.2 mg (range 30-60 mg) and 55.0 mg (range 30-100 mg, p=0.06), respectively, for the prophylaxis group and 83.0 mg (range 30-180 mg) and 85.7 mg (range 30-160 mg, p=0.41), respectively, for the therapeutic group. Weight-based mean starting doses and doses most proximate to delivery were 0.46 and 0.62 mg/kg (p=0.03), respectively, for the prophylaxis group and 0.90 and 0.87 mg/kg (p=0.29), respectively, for the therapeutic group. Dose changes were required in 9 (69%) of 13 pregnancies and 21 (55%) of 38 pregnancies (data from two of the 40 pregnancies were excluded-one in a patient receiving dalteparin, and one in a patient with mitral valve replacement who had higher antifactor Xa goals) in the prophylaxis and therapeutic groups, respectively, to achieve target antifactor Xa activity. The weight-based prophylactic dose was consistently 0.6 mg/kg in all three trimesters, achieving a mean ± SD target antifactor Xa activity of 0.39 ± 0.18 units/ml, whereas the therapeutic dose was 0.9 mg/kg to maintain antifactor Xa activity of 0.71 ± 0.22 units/ml.

CONCLUSION

Dose changes for LMWH throughout pregnancy as guided by antifactor Xa activity were common. A significant increase in the LMWH dose requirements in the prophylactic group suggests that more frequent monitoring of antifactor Xa activity may be appropriate in pregnant patients to maintain target anticoagulant levels.

Fluctuations in anti-factor Xa levels with therapeutic enoxaparin anticoagulation in pregnancy

OBJECTIVE

The objective of the study was to evaluate anti-factor Xa levels with therapeutic enoxaparin anticoagulation in pregnancy.

STUDY DESIGN

A total of 15 pregnant subjects on therapeutic doses of enoxaparin (1 mg/kg +/-20% subcutaneously (s.c.) twice daily (b.i.d.)) were enrolled prospectively in this cross-sectional pilot project. Three blood levels for anti-factor Xa activity were examined: before the enoxaparin dose (trough), 3- to 4-h later (peak) and 8-h later. Anti-factor Xa activity level between 0.5 and 1.2 U/ml was considered therapeutic.

RESULT

Mean anti-factor Xa activity levels were: trough 0.45+/-0.18, peak 0.9+/-0.25 and 8-h after dose 0.72+/-0.23 U/ml. All peak levels were therapeutic; 20% (3/15) of the 8 h and 73% (11/15) of the trough levels were sub-therapeutic.

CONCLUSION

Trough and 8-h post-dose anti-factor Xa activity levels were sub-therapeutic in a substantial number of patients receiving a b.i.d. regimen of therapeutic enoxaparin.

Intrauterine subdural hemorrhage in a preterm neonate possibly associated with maternal low-molecular weight heparin treatment

We report intrauterine subdural hemorrhage in a preterm infant delivered by cesarean section at 32 weeks following vaginal bleeding of a mother treated with low-molecular weight heparin (LMWH) for deep vein thrombosis. The subdural hematomas were partially calcified, proving antenatal occurrence. Maternal trauma during pregnancy, intrauterine infection, cerebral vascular malformation and congenital coagulopathy as known etiologies of subdural hemorrhage could be ruled out. Intrauterine subdural hemorrhage may be an exceptional complication of maternal LMWH treatment.

Venous thromboembolism, thrombophilia, antithrombotic therapy, and pregnancy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This article discusses the management of venous thromboembolism (VTE) and thrombophilia, as well as the use of antithrombotic agents, during pregnancy and is part of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that benefits do, or do not, outweigh risks, burden, and costs. Grade 2 recommendations are weaker and imply that the magnitude of the benefits and risks, burden, and costs are less certain. Support for recommendations may come from high-quality, moderate-quality or low-quality studies; labeled, respectively, A, B, and C. Among the key recommendations in this chapter are the following: for pregnant women, in general, we recommend that vitamin K antagonists should be substituted with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) [Grade 1A], except perhaps in women with mechanical heart valves. For pregnant patients, we suggest LMWH over UFH for the prevention and treatment of VTE (Grade 2C). For pregnant women with acute VTE, we recommend that subcutaneous LMWH or UFH should be continued throughout pregnancy (Grade 1B) and suggest that anticoagulants should be continued for at least 6 weeks postpartum (for a total minimum duration of therapy of 6 months) [Grade 2C]. For pregnant patients with a single prior episode of VTE associated with a transient risk factor that is no longer present and no thrombophilia, we recommend clinical surveillance antepartum and anticoagulant prophylaxis postpartum (Grade 1C). For other pregnant women with a history of a single prior episode of VTE who are not receiving long-term anticoagulant therapy, we recommend one of the following, rather than routine care or full-dose anticoagulation: antepartum prophylactic LMWH/UFH or intermediate-dose LMWH/UFH or clinical surveillance throughout pregnancy plus postpartum anticoagulants (Grade 1C). For such patients with a higher risk thrombophilia, in addition to postpartum prophylaxis, we suggest antepartum prophylactic or intermediate-dose LMWH or prophylactic or intermediate-dose UFH, rather than clinical surveillance (Grade 2C). We suggest that pregnant women with multiple episodes of VTE who are not receiving long-term anticoagulants receive antepartum prophylactic, intermediate-dose, or adjusted-dose LMWH or intermediate or adjusted-dose UFH, followed by postpartum anticoagulants (Grade 2C). For those pregnant women with prior VTE who are receiving long-term anticoagulants, we recommend LMWH or UFH throughout pregnancy (either adjusted-dose LMWH or UFH, 75% of adjusted-dose LMWH, or intermediate-dose LMWH) followed by resumption of long-term anticoagulants postpartum (Grade 1C). We suggest both antepartum and postpartum prophylaxis for pregnant women with no prior history of VTE but antithrombin deficiency (Grade 2C). For all other pregnant women with thrombophilia but no prior VTE, we suggest antepartum clinical surveillance or prophylactic LMWH or UFH, plus postpartum anticoagulants, rather than routine care (Grade 2C). For women with recurrent early pregnancy loss or unexplained late pregnancy loss, we recommend screening for antiphospholipid antibodies (APLAs) [Grade 1A]. For women with these pregnancy complications who test positive for APLAs and have no history of venous or arterial thrombosis, we recommend antepartum administration of prophylactic or intermediate-dose UFH or prophylactic LMWH combined with aspirin (Grade 1B). We recommend that the decision about anticoagulant management during pregnancy for pregnant women with mechanical heart valves include an assessment of additional risk factors for thromboembolism including valve type, position, and history of thromboembolism (Grade 1C). While patient values and preferences are important for all decisions regarding antithrombotic therapy in pregnancy, this is particularly so for women with mechanical heart valves. For these women, we recommend either adjusted-dose bid LMWH throughout pregnancy (Grade 1C), adjusted-dose UFH throughout pregnancy (Grade 1C), or one of these two regimens until the thirteenth week with warfarin substitution until close to delivery before restarting LMWH or UFH) [Grade 1C]. However, if a pregnant woman with a mechanical heart valve is judged to be at very high risk of thromboembolism and there are concerns about the efficacy and safety of LMWH or UFH as dosed above, we suggest vitamin K antagonists throughout pregnancy with replacement by UFH or LMWH close to delivery, after a thorough discussion of the potential risks and benefits of this approach (Grade 2C).

Audit of the peri-delivery use of unfractionated heparin in women on therapeutic low-molecular weight heparin

There is no evidence-based approach for the optimal management of peri-delivery anticoagulation in women receiving therapeutic dose of low-molecular weight heparin (LMWH) during pregnancy. Nevertheless, the maintenance of anticoagulation for the maximal period peri-delivery appears appropriate in women considered to be at high risk of venous or arterial thromboembolism. We developed a regimen based on fixed thromboprophylactic dose of unfractionated heparin (UFH) peri-delivery and undertook an audit to evaluate the use and feasibility of this approach and any adverse events. Fixed intravenous thromboprophylactic dose of UFH (15,000 units/24 h) was commenced on the evening prior to a planned delivery [induction of labour or elective caesarean section (CS)], stopped 4 h predelivery and restarted 2-6 h postdelivery. Compliance was good with 32/38 consecutive deliveries managed according to the regimen. There were no cases of postpartum haemorrhage and no thrombosis associated with these 32 deliveries. Twenty-one patients were delivered by CS (11 elective) and eight patients received epidural/spinal anaesthesia without complication. In conclusion, the fixed thromboprophylactic dose UFH regimen provided maintenance of anticoagulation except for a matter of hours without excessive bleeding risk (conducive to neuroaxial anaesthesia) and was simple, flexible and acceptable to staff and patients.

A descriptive evaluation of unfractionated heparin use during pregnancy

BACKGROUND

The mainstay of oral anticoagulant therapy, warfarin sodium, crosses the placenta during pregnancy and may cause fetal complications. Unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) do not cross the placenta and have demonstrated utility in the prevention and treatment of thrombosis during pregnancy.

OBJECTIVES

The purpose of this study was to review treatment strategy, indication, and maternal and fetal outcomes in anticoagulated pregnancies at Kaiser Permanente Colorado.

PATIENTS/METHODS

We identified 103 pregnancies in 93 mothers prescribed an anticoagulant during a pregnancy occurring between January 1, 1998 and March 31, 2005.

RESULTS

The majority of patients were treated with UFH (89.3%). Indications for anticoagulation included venous thromboembolism (VTE) prophylaxis (53.4%), history of pregnancy loss (29.1%), acute VTE (16.5%), and history of cerebral vascular accident (CVA) (1.0%). There were no maternal deaths. Fetal demise occurred in 8 pregnancies (7.8%) at a median 14 weeks gestation (range 7-22 weeks). No fetal demise occurred in pregnancies treated for acute VTE or history of CVA. There were two occurrences of pulmonary embolism (1.9%) and two hemorrhagic events requiring transfusion (1.9%).

CONCLUSIONS

Maternal and fetal adverse events were infrequent in our population of anticoagulated pregnancies. UFH remains a viable option among more expensive LMWH products.

Thromboembolism in pregnancy

Venous thromboembolism in pregnancy is a clinical emergency that has been associated with significant risk for maternal and fetal morbidity and mortality. The adaptation of the maternal hemostatic system to pregnancy predisposes women to an increased risk of thromboembolism. A timely diagnosis of deep venous thrombosis is crucial because up to 24% of patients with untreated deep venous thrombosis develop a pulmonary embolism. Recent clinical guidelines identify compression venous ultrasound as the best way to diagnose deep venous thrombosis in pregnancy and CT pulmonary angiography as the best way to diagnose pulmonary embolism in pregnancy. Therapy involves supportive care and anticoagulation with unfractionated or low molecular weight heparin, depending on the clinical scenario.

Prevention and management of venous thromboembolism in pregnancy

Normal pregnancy is accompanied by an increase in clotting factors. The resulting hypercoagulable state has likely evolved to protect women from hemorrhage at the time of miscarriage and childbirth. During pregnancy, women are 4 times more likely to suffer from venous thromboembolism (VTE) compared with when they are not pregnant. Relative to pregnancy, the risk postpartum is even higher. The incidence of VTE is approximately 2 per 1,000 births, and VTE accounts for 1 death per 100,000 births, or approximately 10% of all maternal deaths. The most important risk factors during pregnancy are thrombophilia and a history of thrombosis. A history of thrombosis increases the risk for VTE to 2% to 12%. Thrombophilia increases not only the risk for maternal thrombosis but also the risk of poor pregnancy outcome. Despite the increased risk for thrombosis during pregnancy and the postpartum period, most women do not require anticoagulation. Those who do require anticoagulation include women with current VTE, women on lifelong anticoagulation, and many women with thrombophilia or a history of thrombosis. Recommended options for anticoagulation in pregnancy are limited to heparins, which do not cross the placenta. Low-molecular-weight heparin (LMWH) is preferred over unfractionated heparin because LMWH has a longer half-life and is presumed to have fewer side effects. The longer half-life is a disadvantage around the time of delivery, when unfractionated heparin, with its shorter half-life, is easier to manage. For women who develop or are at high risk for heparin-induced thrombocytopenia or severe cutaneous reactions, fondaparinux is probably the agent of choice. Women who do not require lifelong anticoagulation, but require anticoagulation during pregnancy, will still require anticoagulation for the first 6 weeks postpartum.

Pulmonary embolism during and after pregnancy

BACKGROUND

Venous thromboembolic disease is among the most common causes of morbidity and mortality during pregnancy. The clinical evaluation alone is insufficient for the diagnosis of venous thromboembolic disease, and the normal pregnant state makes this evaluation even more challenging.

DIAGNOSIS

Objective testing is the mainstay of diagnosis, including compression ultrasound, impedance plethysmography, ventilation-perfusion scanning, computed tomography scanning, and pulmonary angiography. All of these tests can be safety performed during pregnancy.

TREATMENT

If deep vein thrombosis or pulmonary embolism is diagnosed, anticoagulation should be initiated. Either (unfractionated) heparin or low molecular weight heparin is an acceptable treatment for acute venous thromboembolic disease. Both have risks and benefits, but both can be used safely during pregnancy. Intravenous heparin is the treatment of choice surrounding delivery due to its short half life. Because of the risk of adverse effects on the fetus, warfarin is not generally used during pregnancy. Unstable pulmonary embolism is difficult to treat during pregnancy, as there are minimal data regarding the safety and efficacy of thrombolytic therapy, inferior vena cava filters, and embolectomy during pregnancy. Case reports and case series suggest that thrombolytic therapy may be associated with lower risks of fetal loss than embolectomy.

CONCLUSIONS

Venous thromboembolic disease is a significant cause of morbidity and mortality during pregnancy and the puerperal period. Objective testing is critical to establish the diagnosis and can be safely performed during pregnancy. Anticoagulation with heparin is the mainstay of therapy during the pregnancy, but patients may be transitioned to warfarin after delivery.

Low-molecular-weight heparins for thromboprophylaxis and treatment of venous thromboembolism in pregnancy: a systematic review of safety and efficacy

To assess the safety and efficacy of low-molecular-weight heparins (LMWHs) for thromboprophylaxis and treatment of venous thromboembolism (VTE) in pregnancy, a systematic review of studies to the end of 2003 was undertaken. Data on VTE recurrence and side effects were extracted and cumulative incidences of VTE and adverse effects calculated. Of 81 reports identified, 64 reporting 2777 pregnancies were included. In 15 studies (174 patients) the indication for LMWH was treatment of acute VTE, and in 61 studies (2603 pregnancies) it was thromboprophylaxis or adverse pregnancy outcome. There were no maternal deaths. VTE and arterial thrombosis (associated with anti-phospholipid syndrome) were reported in 0.86% (95% confidence interval [CI], 0.55%-1.28%) and 0.50% (95% CI, 0.28%-0.84%) of pregnancies, respectively. Significant bleeding, generally associated with primary obstetric causes, occurred in 1.98% (95% CI, 1.50%-2.57%), allergic skin reactions in 1.80% (95% CI, 1.34%-2.37%), heparin-induced thrombocytopenia in 0%, thrombocytopenia (unrelated to LMWH) in 0.11% (95% CI, 0.02%-0.32%), and osteoporotic fracture in 0.04% (95% CI, < 0.01%-0.20%) of pregnancies. Overall, live births were reported in 94.7% of pregnancies, including 85.4% in those receiving LMWH for recurrent pregnancy loss. LMWH is both safe and effective to prevent or treat VTE in pregnancy.

Pulmonary embolism and pregnancy

Pulmonary embolism is a significant cause of morbidity and mortality during pregnancy and the puerperium. The spectrum of venous thromboembolism is difficult to diagnose. Objective diagnostic testing is crucial and should not be delayed. Anticoagulation is the mainstay of therapy for deep vein thrombosis and pulmonary embolism. Most of the literature and practice protocols for the treatment of pregnant women are based on data extrapolated from the nonpregnant population, and more research is needed to improve the understanding of the efficacy and safety of testing and therapy in the pregnant population.

A prospective trial that demonstrates that dalteparin requirements increase in pregnancy to maintain therapeutic levels of anticoagulation

OBJECTIVE

The purpose of this study was to determine whether standard therapeutic doses of dalteparin maintain peak therapeutic levels of anticoagulation during pregnancy.

STUDY DESIGN

This was a prospective trial in which 13 pregnancies that required therapeutic anticoagulation were treated with dalteparin 100 U/kg every 12 hours; peak and trough (predose) low molecular weight heparin (anti-Xa activity) levels were monitored every 2 weeks. Dosage adjustments were made to maintain peak anti-Xa activity between 0.5 and 1.0 IU/ml. Bone density and bone turnover markers were measured.

RESULTS

A total of 250 peak and trough low-molecular-weight heparin (LMWH) levels were obtained. Eighty-five percent of pregnancies (11/13) required an upward dosage adjustment. Trough levels were in the therapeutic range only 9% of the time, despite the maintenance of therapeutic peak levels. Bone resorption markers and density were unchanged in singleton pregnancies.

CONCLUSION

Dalteparin dosing, based on weight alone, every 12 hours is inadequate to maintain most pregnant women in the therapeutic range throughout pregnancy as measured by anti-Xa activity. Trough levels are rarely in the therapeutic range, despite maintenance of therapeutic peak levels. These notable changes in low molecular weight heparin peak may explain reported failures in pregnancy.

Deep vein thrombosis after elective cesarean section

INTRODUCTION

Pregnancy is associated with an overall 5-10 fold increased risk of venous thromboembolism (VTE). The absolute risk is highest during and shortly after delivery. Although operative delivery further increases the risk of VTE, there is no consensus on thromboprophylaxis after an elective cesarean. The aim of the present study was to investigate the frequency of symptomatic and asymptomatic deep venous thrombosis (DVT) in a low risk cesarean section population.

MATERIALS AND METHODS

Fifty-nine women undergoing elective cesarean section were screened for DVT using triplex Doppler sonography 3-5 days after delivery. Markers of activated coagulation were also followed and all women were screened for thrombophilia. Postoperative thromboprophylaxis was not given. During the same period all cases of symptomatic VTE were also recorded.

RESULTS

No DVT was detected by ultrasonography and no women developed symptomatic VTE during the six weeks follow-up period after delivery. Six women had thrombophilia. During the study period, a cesarean section was performed in 1067/5364 (20%) deliveries. Five of these women (0.47%) developed symptomatic pulmonary embolism, and all of these women had additional risk factors for VTE.

CONCLUSION

The risk of DVT among healthy pregnant women undergoing elective cesarean section is low, and general medical thromboprophylaxis is probably not justified.