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Thrombophilia, or a genetic or acquired tendency to clot more than usual, is one of the most frequently tested for and most widely misunderstood conditions in pregnancy. On this episode of the Healthful Woman podcast, Dr. Andrei Rebarber joins Dr. Nathan Fox to untangle what these clotting predispositions actually mean, why testing has exploded far beyond what the evidence supports, and how doctors decide who really needs treatment.

Genetic vs. Acquired Thrombophilias

Dr. Rebarber explains that the body normally keeps a careful balance between clotting and unclotting, a balance shaped by both genetics and everyday factors like body weight, smoking, and immobility. Pregnancy itself tips that balance toward clotting, since the body evolutionarily prepares for the blood loss of delivery. Within that context, there are two broad categories worth knowing: inherited thrombophilias, like Factor V Leiden and the prothrombin gene mutation, which are simply predispositions rather than diseases, and acquired conditions like antiphospholipid antibody syndrome, an autoimmune disorder with a much stronger and more dangerous association with pregnancy complications like stillbirth and severe preeclampsia.

The Trouble With Testing

Despite genetic thrombophilias being common, affecting roughly 5 to 10 percent of people, most carriers never develop a clot in their lifetime. Dr. Rebarber notes that testing has nonetheless become widespread across specialties, often without proper counseling beforehand. Protein S testing, for example, is notoriously unreliable during pregnancy since normal pregnancy hormones lower Protein S levels on their own, frequently producing false positives. The MTHFR mutation, in particular, draws unnecessary alarm; the two doctors agree it is a benign, common variant that current guidelines say should not routinely be tested at all. As Dr. Rebarber puts it, the real question before ordering any of these tests should be, “how would you treat me different if I’m positive.”

Who Actually Needs Treatment

The doctors walk through how they decide who genuinely benefits from testing and treatment: primarily women with a personal history of an unexplained blood clot, a strong family history, or a severe obstetric history like early-onset preeclampsia, stillbirth, or significant growth restriction. Most patients who test positive fall into a low-risk category and need nothing more than a daily baby aspirin, which decades of data show carries essentially no downside for mother or baby. A smaller group, generally those with a personal clotting event or artificial heart valve, may need injectable anticoagulants like Lovenox, which carry their own tradeoffs including bruising, rare allergic reactions, and the need to switch medications near the end of pregnancy so an epidural remains an option during labor.

Listen to the Healthful Woman Podcast

Dr. Rebarber sums up the larger lesson simply: a positive thrombophilia test is only one piece of a much bigger clinical picture, and the goal isn’t to treat a lab value, it’s to understand the whole story behind it. To hear the complete conversation, including a deeper dive into antiphospholipid antibody syndrome and how these decisions play out around labor and delivery, listen to “Thrombophilia in Pregnancy: The Clot Thickens…” on the Healthful Woman podcast.

If you have questions about thrombophilia testing or need specialized care during a high-risk pregnancy, schedule an appointment with our team. We are here to help you navigate these decisions with clear, individualized guidance.

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!