VTE in pregnancy

ACEM Fellowship

Table of Contents

Introduction

Leading cause of maternal mortality in developed countries
1/1600 pregnancies (0.06 – 8%)
5-10% incidence if previous VTE during pregnancy ! Risk increased 4-50x non-pregnant females ! Why confusion?
SOB, leg swelling, tachycardia all physiological in pregnancy
Well’s score, PERC cannot be used in pregnant patients
D-dimer rises from second trimester and remains elevated for 4-6 weeks postpartum
60% of healthy females have raised D-dimer in pregnancy
Particular risk of left pelvic/iliac vein thrombosis
Particularly high risk in post-partum period (for 13-18 weeks)
4x higher risk in first 6 weeks post-partum and 80% occur in first 3 weeks post-partum
DVT left sided in 70-90%
65% of thrombi involve ileofemoral vessels with higher risk of embolism
Isolated pelvic thrombi occur in 10% (<1% in general population)
D-dimer falls to normal levels 4-6 weeks post-partum
Pregnancy-adjusted D-dimer not prospectively validated
NPV of D-dimer is still high so could potentially use to rule out although a previous study showed a negative D-dimer was not 100% sensitive

Factor V Leiden – 3x risk in pregnancy (up to 50x = 10% risk if first-degree relative with VTE though)
Antithrombin III, Protein C or S deficiency – 8x risk
Antiphospholipid syndrome – 5% risk of VTE in pregnancy
Present and responsible (at least in part) for 50% of VTE in pregnancy
Most important determinant of risk is personal or family history of VTE

Thrombophilia in Pregnancy Prophylaxis Study
292 pregnant women with thrombophilia or previous placental complications randomised to prophylactic dalteparin vs. placebo with no difference in outcomes

Screening of asymptomatic populations is NOT recommended due to low frequency of the condition becoming symptomatic and lack of safe, costeffective, long-term method of prophylaxis against VTE
Screening recommended for women planning pregnancy (UpToDate):
Hx of VTE with transient risk factor: If negative screen, do not need antenatal prophylaxis
Hx of VTE (unprovoked, recurrent or associated with COCP/pregnancy):
Relatively high risk and should receive thromboprophylaxis regardless of thrombophilia testing BUT screening alters thromboprophylaxis regime
No prior VTE but first-degree relative with high-risk thrombophilia:

If PE most likely diagnosis, high-risk gestalt = progress to imaging
If other diagnoses equally likely and patient in first trimester = Do D-dimer and if negative, can stop there
If high-risk or has a positive D-dimer = CXR
May show alternative diagnosis and helps decide between VQ and CTPA ! Then do duplex USS lower limbs
If positive, treat for PE
VT or CTPA
- Risk of death from undiagnosed PE much higher than risk of malignancy due to radiation
- VQ may not be definitive – Dunn states 97% of results are diagnostic though if no asthma/chronic lung disease and normal CXR
The foetus
- General consensus is that dose of 0.1Gy during gestation is threshold for congenital abnormalities (although no validation of this)
- Both VQ and CTPA are below this (VQ slightly higher)
- Iodine contrast has theoretical risk to foetal thyroid (no studies investigating this)
- Childhood cancer risk 1/280 000 vs. <1 in a milllion for CTPA
The mother
- CTPA exposes breasts to high radiation dose (increases lifetime risk by 14% = 20 per 100 000)
- Radiation dose of VQ scan can be reduced by performed half-dose perfusion scan and only proceeding to ventilation scan if abnormality detected + IDC to drain radiation urine
- If CXR normal, recommendation is half-dose perfusion scan. If CXR abnormal, CTPA recommended

Heparin
- Does not cross placenta
- Bleeding at uteroplacental junction still possible
LMWH
- Also does not cross placenta and is preferred agent. Treatment until 6 weeks post-partum
NOAC’s cross placenta and may cause congenital abnormalities
IVC filters
- Indications same as non-pregnant
- Acute VTE and anticoagulation contraindicated
- Episode of acute VTE while anticoagulated
- Critically ill at risk of recurrent embolism that would likely prove fatal
If haemodynamically unstable
- Thrombolysis/embolectomy are controversial
  - 30% risk of non-fatal maternal major bleeding
  - 38% risk of preterm labour
  - 15% risk of placental abruption and fetal demise
- Consider option of delivery of baby if nearing term prior to thrombolysis with subsequent management of bleeding in liaison with obstetric team
- Embolectomy an option if thrombolysis is otherwise contraindicated e.g. previous ICH, coagulopathy or intracranial mass
If arrested and >20 weeks perform resuscitative hysterotomy to deliver baby followed by thrombolysis and management of subsequent bleeding
ECMO may play a role in centres capable of this if ongoing severe haemodyamic instability and not a lysis candidate

Hunt et al. performed a prospective study and found no diagnostically useful threshold of D-dimer to diagnosing or ruling out VTE in pregnancy.

500 pregnant women in prospective randomised study
3 factors considered:
- Clinical signs of DVT – Had duplex USS performed
- Haemoptysis
- PE most likely diagnosis
Algorithm
- No YEARS criteria and D-dimer <1000 – Ruled out
- No YEARS criteria and D-dimer >1000 – CTPA
- Any YEARS criteria and D-dimer <500 – Ruled out
- Any YEARS criteria and D-dimer >500 – CTPA
Results
- 1 DVT missed and no PE missed at follow-up
- CTPA avoided in 65% of first-trimester and 32% of third trimester women

Last Updated on August 12, 2022 by Andrew Crofton