Thrombosis in Pregnancy
The timing of the previous VTE history is important when deciding on the anticoagulant dose in pregnancy. In pregnant women with a VTE that occurred within the previous 4 to 6 weeks, full-dose anticoagulation with LMWH should be considered; an intermediate dose (three-fourths of a therapeutic dose) may be used if the thrombotic episode occurred more than 6 weeks earlier but still within a year. Prophylactic dosing may be sufficient if the episode occurred more than a year earlier.90 A clinical trial (High-Low) is under way to explore the optimal dose of LMWH in pregnant women with prior history of VTE who are not on chronic anticoagulation therapy.91
How is anticoagulation therapy managed in the peripartum period?
Neuraxial anesthesia during active labor while on anticoagulation increases the risk for central nervous system bleeding. Therefore, if spontaneous labor occurs in women on therapeutic dose anticoagulation, neuraxial anesthesia cannot be used. However, in the event of elective induction of labor or caesarean section, neuroaxial anesthesia may be performed 12 hours after the administration of the last prophylactic dose of LMWH or 24 hours after the last therapeutic dose of LMWH. Intravenous UFH should be stopped for 6 hours before induction of labor with a confirmed normal aPTT before placement of neuraxial anesthesia. There is no contraindication for using neuraxial anesthesia during subcutaneous standard UFH at total doses of 10,000 units daily. The risk of spinal hematoma with larger daily subcutaneous doses is unclear; therefore, a documented normal aPTT must be obtained before placement of neuroaxial anesthesia.
,Postpartum, reinitiation of prophylactic-dose LMWH should be delayed for at least 12 hours after the removal of an epidural catheter. Therapeutic-dose LMWH should be administered no earlier than 24 hours after neuraxial anesthesia, providing that proper hemostasis is achieved. In the absence of persistent bleeding, if no regional anesthesia was used, LMWH may be resumed 12 hours after delivery.92 Anticoagulation with either LMWH or warfarin is recommended for at least 6 to 12 weeks postpartum.33
COUNSELING
Patients should be advised to manage controllable risk factors, including avoiding prolonged immobilization, avoiding excessive weight gain in pregnancy, and stopping smoking. Periods of immobilization tend to cause reduced blood flow (stasis), which predisposes to thrombosis. In a systematic review of records of all patients with confirmed PE after arrival at Charles de Gaulle airport in Paris during a 13-year period, women had a higher risk of PE after a long-distance flight than men, with an estimated incidence of 0.61 per million passengers versus 0.20, respectively; the incidence reached 7.24 and 2.35 cases, respectively, in passengers traveling more than 10,000 kilometers.93,94
The risk of air travel-related thrombosis in pregnant women is estimated to be between 0.03% and 0.1%. Physicians must decide on an individual basis how to prevent travel-related thrombosis in their pregnant patients. In most passengers, prevention can be limited to encouraging exercise, avoidance of long sleeping periods, and not using a window seat. Women at high risk for VTE, such as women with a prior history of VTE who are not on anticoagulation or women with known asymptomatic thrombophilia or other risk factors for thrombosis such as obesity, may benefit from a short period (1–3 days) of LMWH starting 2 hours before a long-distance flight.95
Activation of the coagulation system has been demonstrated in cigarette smokers.96 Heavy smoking was found to be a significant risk factor for VTE in a cross-sectional analysis of 2404 men and women.97 An increased risk for thrombosis during pregnancy is seen in cigarette smokers15,98 and is enhanced with the concomitant use of illicit drugs.99 Other obstetric complications associated with smoking and illicit drug use during pregnancy include preterm labor, spontaneous abortion, perinatal death, low birth weight, and abruption placenta. The efficacy of nicotine replacement therapy in pregnancy is uncertain.100 Recommendations are to advise patients to stop smoking, obtain psychosocial counseling, and utilize adjunctive therapies, which have been shown to have some effect on abstinence rates.101
CONCLUSION
Women are at increased risk for VTE during pregnancy and the postpartum period. Awareness of risk factors and the signs and symptoms of VTE is paramount. Prompt diagnosis and treatment is mandatory to decrease complications of VTE. LMWH is the mainstay treatment of VTE in pregnancy, as it does not cross the placenta. Both LMWH and warfarin are safe during lactation. Close communication among the patient, obstetrician, hematologist, anesthesiologist, and neonatologist is crucial to optimize the care of these patients.
