Deep venous thrombosis in a preterm newborn of a mother with activated protein C resistance

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.

Low molecular weight heparins: a guide to their optimum use in pregnancy

The incidence of pulmonary embolism (PE) and venous thromboembolism (VTE) is higher in pregnant patients than in non-pregnant patients. The incidence of thrombosis in all pregnancies is reported to be between 0.05 and 1%, and an incidence as high as 3% may be present in women after caesarean section. Anticoagulant medication is prescribed during pregnancy in patients presenting with VTE, thrombophilia abnormalities, or a history of PE or VTE. Since unfractionated heparin (UH) does not cross the placental barrier, it has become the gold standard anticoagulant therapy during pregnancy. Oral anticoagulants may also be prescribed during the second trimester but they cross the placental barrier. Low molecular weight heparins (LMWH) are effective, easy to use and have good safety profiles. The practical conditions of use have yet to be validated for pregnancy settings. In the absence of an approved indication, LMWH use during pregnancy is therefore the responsibility of the practitioner. However, several studies on LMWH as prophylaxis for PE or VTE have shown that such products are effective with good safety. Moreover, LMWH use is associated with reduced frequencies of thrombocytopenia and osteoporosis compared with UH use. Very few studies on LMWH use for the treatment of PE or VTE during pregnancy have been published, but the safety of LMWH use in this setting appears to be good. The review of the use of LMWH in pregnancy settings includes recommendations on the practical conditions of use. In the absence of large-scale, randomised, double-blind trials in such settings (which are needed), we propose the use of LMWH as prophylaxis for PE and VTE during pregnancy, but not for the treatment of these conditions. In prophylaxis settings, dalteparin sodium and enoxaparin sodium have been the most widely studied LMWH and we believe that priority should therefore be given to those products. Pending approval of LMWH for use in pregnancy, the use of LMWH off-label is the practitioner's responsibility.

Use of enoxaparin in a preterm infant

OBJECTIVE

To describe the use of enoxaparin to treat suspected thrombosis in a preterm neonate.

CASE DESCRIPTION

A 29-week-gestation white infant with a family history of protein S deficiency lost color and blood flow to the right hand several hours after removal of the umbilical artery catheter. Although normal color returned to all except the distal first, second, and third fingers after warming, Doppler flow showed a radial artery defect, indicating a lack of blood flow. Enoxaparin 1 mg/kg intravenously every eight hours was then started. Heparin concentrations measured via anti-Xa assay drawn four and eight hours after a dose were 0.78 and 0.39 units/mL, respectively. Pharmacokinetic parameters calculated from these concentrations using a one-compartment model were elimination half-life four hours, volume of distribution 0.13 L/kg, and clearance 0.022 L/kg/h. No adverse effects were noted. Blood flow eventually returned, leaving only the third fingertip chronically injured.

DISCUSSION

Differences between the neonatal and adult hemostatic systems contribute to an increased risk of thromboembolic events and an altered sensitivity to heparin anticoagulation in the neonate. Although heparin is currently the anticoagulant of choice, it may produce several adverse effects, such as hemorrhage and thrombocytopenia, which may be avoided by use of low-molecular-weight heparins (LMWHs). However, despite the efficacy and improved safety profile of LMWHs in adults, data regarding their use in children and neonates are scarce. This case demonstrates that enoxaparin can be used safely and effectively in a preterm infant through appropriate monitoring of heparin concentrations to adjust dosages. A larger volume of distribution of enoxaparin was noted in this neonate than in adults.

CONCLUSIONS

Enoxaparin 1 mg/kg intravenously every eight hours was used safely in this preterm infant with suspected thrombosis, suggesting that more than one dosing regimen may be appropriate in this population.

Low-molecular-weight heparins in pregnancy

We conducted a systematic review, with MEDLINE and Cochrane Library data base searches and bibliographic reviews, of English-language reports describing therapy with low-molecular-weight heparin (LMWH) in pregnancy. Altogether 40 citations, excluding abstracts, were identified. When the quality of evidence was categorized according to the method outlined by the U.S. Preventive Services Task Force, 2 articles were level I, 3 were level II-1, 3 were level II-2, 4 were level II-3, 9 were level III, and the remaining 19 were classified as other (i.e., below level III). Of the 728 pregnant women and 1 postpartum woman described in the 40 citations, 340 (47%) received dalteparin, 192 (26%) enoxaparin, 108 (15%) certoparin, 54 (7%) nadroparin, 30 (4%) other LMWH, and 6 (< 1%) unspecified. The indication for LMWH in most patients (606 pregnancies, 83%) was for thromboprophylaxis. Daily doses ranged from 2500-22,000 U for dalteparin, 20 mg (2000 U)-80 mg (8000 U) for enoxaparin, 3000 U for certoparin, and 2050-15,000 U for nadroparin. Regimens included fixed dosages, increasing dosages as pregnancy progressed, dosages based on body weight, and dosages titrated according to anti-Xa levels. Duration of therapy ranged from a single dose to 476 days. Maternal anti-Xa levels were reported for 255 pregnancies. Target anti-Xa levels ranged from 0.1-0.6 U/ml and measured values from 0.0-0.7 U/ml. Major maternal findings were 18 local and generalized skin reactions, 27 bleeding complications, 9 thromboembolic events, 8 deep vein thromboses, 1 bilateral renal vein thrombosis, 4 pulmonary emboli, 1 hepatic infarction, 4 cases of thrombophlebitis, 12 cases of preeclampsia, 1 placental abruption, and 2 osteoporotic vertebral fractures. A major fetal finding was lack of anti-Xa activity in fetal or cord blood. Published experience suggests that LMWHs are generally safe and effective when administered for thromboprophylaxis during pregnancy. Until prospective, randomized, controlled trials comparing them with unfractionated heparin are performed, their benefits in pregnancy will remain inconclusive.