Precautions for the mother with a history of DVT or PE

If a woman was treated for DVT or pulmonary embolism in one pregnancy, does she need to take any special precautions in future pregnancies? Opinions on this differ.

There is consensus that any woman with a history of pulmonary embolism in the past should start preventative heparin injections as soon she finds out she is pregnant. This advice is also relevant for those considered to be high-risk for other reasons (see above)

The high-risk group also includes those with confirmed thrombophilia syndrome and those who have a history of two or more episodes of thrombosis in the past. This is regardless of whether the episodes occurred during pregnancy or not.

For those who have had DVT in the past when not pregnant but are otherwise deemed to be low-risk, the policy is less clear-cut and the attending doctor will, in most cases, decide on an individual basis.

What constitutes DVT low-risk

If there is only one episode of uncomplicated DVT in the mother's past history, it is considered low-risk. However, if there is an additional risk factor, such as obesity, smoking, or she has had several children (multiparity), the attending doctor may advise the use of heparin as a preventative measure. The general rule in obstetrics is that; a combination of two or more low risk factors constitutes a high risk.

DVT Risk: Precautions to be taken during labor and delivery

All women at high-risk will already be on some form of heparin during pregnancy. This will need to continue during labor and delivery, with some minor scheduling adjustments. For identified low-risk patients (see above), who may not have been on any preventative treatment, many experts agree that a short course commenced at the onset of labor and continued for a few weeks post-natally is a good idea. Again, this has to be individualized. It is important to bear in mind that the postnatal period is a particularly high risk one for DVT development.

Post-delivery, the mother may opt to switch from injections to warfarin tablets, or she may decide to carry on with injections.

Delivery by cesarean section with DVT risk

In this case, the advice is clear. Both low- and high-risk patients are given some form of heparin. Operative delivery (cesarean section) is a recognized risk factor for thrombosis in its own right and anybody with a previous history has to be protected.

The preventative measure is extended to those women with no previous history of thrombosis but who have an independent risk factor, such as being overweight. Some experts take the view that this should be given to all mothers undergoing a cesarean section.

DVT treatment post-delivery

Because the risk posed by pregnancy does not disappear immediately after delivery, treatment is and should continue post-delivery. In fact, in comparative terms, the immediate post-partum period is the riskiest.

The 6 to 8 weeks of treatment adopted by most units is arbitrary, because it has always been difficult to know when it is entirely safe to stop altogether; the figure has more to do with consensus than science.