Thrombophilia (Hereditary Clotting Defect) is defined as the genetic predisposition to developing intravascular thrombosis. It is due to hypercoagulability of blood leading to impairment of initial vascularization that takes place during implantation.

Thrombophilia affects as many as one in five people in the United States and is responsible for pregnancy loss (most particularly after the 1st trimester) and “unexplained” infertility, as well as being a factor in some cases of “unexplained” IVF failure. Whether (and/or the extent to which) thrombophilia causes 1st trimester recurrent pregnancy loss (RPL) is the subject of debate and is controversial. In fact, first-trimester RPL is far more likely to be due to immunologic implantation dysfunction (IID) and/or irregularities in the contour of the uterine cavity or insufficient thickness of its lining (a thin endometrium). Thrombophilia has also been associated with late pregnancy-induced complications such as preeclampsia, premature separation of the placenta (abruptio placenta), placental insufficiency with intrauterine growth retardation, and in “unexplained” intrauterine death.

This having been said, it is a fact that most women with a thrombophilia go on to experience healthy pregnancies.

Diagnosis of Throbophilia

Thrombophilia is diagnosed when one or more of the following is detected:

  • Mutational defect involving methylenetetrahydrofolate reductase (MTHFR), which occurs in at least 20% of affected cases. Homozygosity for a common C677T mutation in the MTHFR gene that is associated with hyperhomocysteinemia is the most common form of hereditary thrombophilia leading to a 3-fold increase in risk of complications.
  • Mutation of factor V Leiden (FVL),
  • A mutation of prothrombin G20210A,
  • Deficiency of antithrombin III
  • Deficiency of protein C
  • Deficiency of protein S

Risk Factors

  • Pregnant women with predisposing factors such as:
  • A personal or family history of thromboembolism (deep vein thrombosis), pulmonary embolism (blood clot in the lung), cerebrovascular accidents (i.e. strokes)
  • A personal history of pregnancy complications such as unexplained intrauterine death, preeclampsia, abruptio placenta, intrauterine growth retardation, placental insufficiency, should be tested for the condition.


Treatment should be initiated as soon as possible after pregnancy is diagnosed biochemically (blood or urine hCG test) and be continued throughout gestation.

Severe thrombophilias (e.g. homozygous MTHFR mutations, protein C deficiency, prothrombin G20210A mutation) as well as cases of mild thrombophilias associated  with one or more of the pregnancy complications mentioned above, are best treated with low-molecular weight heparin (LMWH).

For other (milder) thrombophilias and no history of prior pregnancy complications: Low-dose aspirin with the B vitamins folic acid, B6 and B12.