Which agents should be used for thromboprophylaxis?

Low-molecular-weight heparin (LMWH)

LMWHs are the agents of choice for antenatal and postnatal thromboprophylaxis. Doses of LMWH are based on weight. For thromboprophylaxis the booking or most recent weight can be used to guide dosing. [New 2015] It is only necessary to monitor the platelet count if the woman has had prior exposure to unfractionated heparin (UFH). Monitoring of anti-Xa levels is not required when LMWH is used for thromboprophylaxis. Doses of LMWH should be reduced in women with renal impairment. LMWH is safe in breastfeeding.

Contraindications to LMWH

LMWH should be avoided, discontinued or postponed in women at risk of bleeding after careful consideration of the balance of risks of bleeding and thrombosis. Women with previous or current allergic reactions to LMWH should be offered an alternative preparation or alternative form of prophylaxis. [New 2015] Further advice on the management of a woman with both VTE risk factors and bleeding risk factors or LMWH allergy may be sought from a haematologist with expertise in the management of thrombosis and bleeding disorders in pregnancy.

Unfractionated heparin

In women at very high risk of thrombosis (see Appendix IV), UFH may be used peripartum in preference to LMWH where there is an increased risk of haemorrhage or where regional anaesthetic techniques may be required. If UFH is used after caesarean section (or other surgery), the platelet count should be monitored every 2–3 days from days 4–14 or until heparin is stopped.


Potential use of danaparoid should be in conjunction with a consultant haematologist with expertise in haemostasis and pregnancy.


Fondaparinux should be reserved for women intolerant of heparin compounds. Fondaparinux use in pregnancy should be in conjunction with a consultant haematologist with expertise in haemostasis and pregnancy. Fondaparinux should be considered if there is severe cutaneous heparin allergy or HIT (no Grade).

ACOG Practice bulleting no 123: thromboembolism in pregnancy Obstet Gynecol 2011 Sep 118(3) 718-29.

Low-dose aspirin

Aspirin is not recommended for thromboprophylaxis in obstetric patients. For women who fulfill the laboratory criteria for 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 UFH or prophylactic LMWH combined with low dose aspirin, 75 to 100 mg/d, over no treatment (Grade 1B). For women considered at risk of preeclampsia, we recommend low-dose aspirin throughout pregnancy, starting from the second trimester, over no treatment.

CHEST 2012: 141(2)suppl:e691S -e736S.


Warfarin use in pregnancy is restricted to the few situations where heparin is considered unsuitable, e.g. some women with mechanical heart valves. Women receiving long-term anticoagulation with warfarin can be converted from LMWH to warfarin postpartum when the risk of haemorrhage is reduced, usually 5–7 days after delivery. Warfarin is safe in breastfeeding.


Dextran should be avoided antenatally and intrapartum because of the risk of anaphylactoid reaction.

Oral thrombin and Xa inhibitors

Non-vitamin K antagonist oral anticoagulants (NOACs) should be avoided in pregnant women. Use of NOACs is not currently recommended in women who are breastfeeding.

Anti-embolism stockings

The use of properly applied anti-embolism stockings (AES) of appropriate size and providing graduated compression with a calf pressure of 14–15 mmHg is recommended in pregnancy and the puerperium for women who are hospitalised and have a contraindication to LMWH. These include women who are hospitalised post-caesarean section (combined with LMWH) and considered to be at particularly high risk of VTE (e.g. previous VTE, more than four risk factors antenatally or more than two risk factors postnatally) and women travelling long distance for more than 4 hours.