Question

Deep vein thrombosis in pregnancy is best treated by

• A. Heparin in the 1st trimester and warfarin in the 2nd and 3rd trimesters
• B. Warfarin in all trimesters
• C. Heparin in all trimesters
• D. Heparin in the 1st and 2nd trimesters and warfarin in the 3rd trimester

Hint:

Remember which drug crosses the placenta and when the embryopathy risk is highest.

Answer 1

The Correct Option is A

This question is about timing anticoagulant drugs correctly across the three trimesters of pregnancy to protect the developing fetus while still treating the clot.

1. Heparin in the 1st trimester, warfarin in the 2nd and 3rd: Heparin does not cross the placenta, so it protects the fetus during the organ forming weeks of the first trimester. Warfarin is then used later, once past the window where it would cause warfarin embryopathy, such as nasal hypoplasia and abnormal bone stippling.
2. Warfarin in all trimesters: This leaves the fetus exposed to warfarin during the first trimester organ forming period, risking embryopathy, so it is not the safest choice.
3. Heparin in all trimesters: This avoids fetal drug exposure completely and is increasingly favored in modern practice for treating DVT in pregnancy, but the classic teaching point in this question is the stepwise heparin to warfarin switch.
4. Heparin in the 1st and 2nd trimesters, warfarin only in the 3rd: This does not fit the standard reasoning, since the concern in the third trimester is warfarin's effect on fetal and neonatal bleeding around the time of delivery, which is exactly when it should be avoided rather than started.

The classic stepwise answer keeps the fetus away from warfarin exactly in the first trimester, when the embryopathy risk is highest, then allows warfarin afterward.

Let's summarize:

• Warfarin is avoided in the first trimester because it can cause embryopathy.
• Heparin is the safe substitute early in pregnancy since it does not cross the placenta.

So the answer taught for this question is heparin in the first trimester followed by warfarin in the second and third trimesters.