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

Step 1: Recall why warfarin is a problem in pregnancy.
Warfarin crosses the placenta, and reaching the fetus in the first trimester, roughly weeks 6 to 12, can cause warfarin embryopathy, with nasal hypoplasia and abnormal bone stippling (chondrodysplasia punctata). This is why warfarin is avoided in the first trimester of pregnancy.

Step 2: Recall why heparin is used instead in early pregnancy.
Heparin is a large molecule that does not cross the placenta, so it does not carry this teratogenic risk. It is the anticoagulant of choice while the fetus is forming its organs in the first trimester.

Step 3: Understand why warfarin was traditionally allowed later in pregnancy.
Once the period of organ formation is over, in the classical stepwise regimen taught for anticoagulation in pregnancy, warfarin was considered an option for the middle and later part of pregnancy since the embryopathy risk window has passed.

Step 4: Rule out the other options.
Warfarin throughout pregnancy exposes the fetus to first trimester embryopathy risk, so giving it in all trimesters is unsafe. Heparin throughout pregnancy is increasingly preferred in current practice for treating a plain DVT, since it avoids fetal warfarin exposure altogether, but the classical teaching point tested here is the stepwise switch from heparin to warfarin. Heparin for the first two trimesters with warfarin only in the third does not fit either, since starting warfarin close to delivery raises the risk of fetal and neonatal bleeding at exactly the wrong time.

Final Answer:
The teaching point tested is the classic stepwise plan, heparin during the first trimester to avoid warfarin embryopathy, then warfarin in the second and third trimesters.
\[ \boxed{\text{Heparin in the 1st trimester and warfarin in the 2nd and 3rd trimesters}} \]