Patient Education Blog

Pregnancy and Blood Clots: Prevention, Diagnosis, Treatment

A new guideline about the prevention, diagnosis, and treatment of DVT and PE associated with pregnancy was published today by ACOG (American College of Obstetricians and Gynecologists) in its respected series of Practice Bulletins.  The bulletin also takes detailed reference to prevention of blood clots in pregnant women with thrombophilia.  Unfortunately, the guidline is not publically available – access requires a subscription to the journal Obstetrics & Gynecology.  However, the key points are as follows:


  • Doppler ultrasound of the legs is the diagnostic test for suspected DVT.
  • If Doppler ultrasound is negative or equivocal, MRI scanning of the leg/pelvis is recommended.
  • D-dimer blood  test is not helpful.
  • When working up supsected PE, a nuclear medicine VQ scan or chest CT are the diagnostic test of choice, both associated with relatively low radiation exposure for the unborn.
  • Two good, comprehensive, practical tables (ACOG table 2 and 3) are provided in the Bulletin with recommendations as to which patient to treat (table 2) and what drugs and doses to use (table 3) to prevent blood clots.  Reference is taken to pregnancies in women with and without thrombophilia, with and without previous blood clots, and the ante- and postpartum management.
  • For routine prophylactic low molecular weight heparin (LMWH) dosing, blood tests to monitor the LMWH level (called anti-Xa levels) are not needed.
  • For full dose LMWH therapy, it is not clear whether anti-Xa laboratory monitoring is beneficial and whether LMWH dose adjustment based on anti-Xa levels is needed.
  • Women on lower-dose prophylactic or full-dose therapeutic LMWH may be converted from LMWH to the shorter half-life unfractionated heparin in the last month of pregnancy or sooner if delivery appears imminent (to allow for safer epidural analgesia).
  • Epidurals  should be withheld for 10-12 hours after the last prophylactic dose of LMWH or 24 hours after the last therapeutic dose of LMWH.
  • If anticoagulation is needed in the postpartum period, it should be resumed no sooner that 4-6 hours after vaginal delivery or 6-12 hours after C-section, to minimize bleeding.  Pneumatic compression devices should be used peripartum until anticoagulation is restarted.
  • C-section:
    • All women undergoing C-section delivery should have pneumatic compression devices placed BEFORE delivery (unless they are on pharmacologic VTE prophylaxis already).
    • Women undergoing C-section who have additional VTE risk factors may require LMWH or unfractionated heparin prophylaxis in addition to pneumatic compression devices.
  • Breast feeding is fine on LMWH, unfractionated heparin and warfarin, as these drugs do not accumulate in breast milk.


Thromboembolism in Pregnancy. Obstetrics & Gynecology. 118(3):718-729, September 2011.  Practice bulletin # 123.

Disclosures:  I have no financial conflict of interest relevant to this post.

Last updated: August 24th, 2011

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3 Responses to “Pregnancy and Blood Clots: Prevention, Diagnosis, Treatment”

  1. natalie says:

    I’m so glad this has been published. Has ACOG provided any guidelines as to how to prevent clots in pregnant women who are put on bedrest? It seems there is no “standard” of practice in that area, sadly.

  2. julie says:

    It’s too bad the ACOG table only addresses DVT & PEs. I have never had a clot, but have Factor V Leiden (heterozygous) and have had 3 miscarriages (two consecutive 2nd trimester losses). I am on LWMH with the current pregnancy to prevent clots forming in the placenta & causing another fetal death.

    Even still, I appreciate the excellently written article.

    • Stephan Moll says:

      This issue is addressed, to some degree, in another ACOG Bulletin publication also published this week (Bulletin #124. “inherited Thrombophilias in Pregnancy”. Obstet Gynecol 2011;118:730-740. The Bulletin states that “Inherited thrombophilia testing in women who have experienced recurrent fetal loss or placental abruption is not recommended because it is unclear whether anticoagulation reduces recurrence”.

      My assessment of and approach to this clinical issue is different to the #124 ACOG bulletin. It is discussed on Clot Connect at