Frequency of factor V(Leiden) and prothrombin G20210A in placentas and their relationship with placental lesions.

The most common hereditary hypercoaguable states are factor V(Leiden) (FVL) and prothrombin mutations (PRO). FVL and PRO present with an incidence of approximately 5% in a heterogeneous population, and 45% to 63% of the thrombophilic population. The frequency of these mutations in the fetal population and their clinical importance is unknown. Fetal side thromboembolic events (FST) include congenital stroke and renal vein thromboses. In some cases, FST can be diagnosed by placental histopathology when avascular (infarcted) villi are present in a patent maternal vascular space. FST can present as placenta-fetal-vascular or fetal-visceral-vascular lesions. Causes include vascular damage from cord compression or inflammation, but most remain unclear. Potential causes of FST include FVL and PRO. We describe the incidence of FVL and PRO from a prospective group of 169 consecutive placentas and in a retrospective group of archived placentas diagnosed with placental FST. One each of FVL and PRO heterozygosity was found in the prospective set (< 1% incidence for each). Five prospective placentas were diagnosed with placental FST, for an incidence of 3%; all were wild-type for FLV and PRO. Twenty-seven of 65 archived FST cases had analyzable DNA to find 5 FVL heterozygotes (18.5%); all were wild-type for PRO. Twenty-one of 65 retrospective archived controls analyzable found 1 case of FVL heterozygosity (< 5%). We find that the frequency of FVL and PRO may be decreased in the pregnant population but increased in cases of placental FST. Because factor V Leiden heterozygosity carries an increased risk for thrombotic complications, we suggest placental diagnosis of fetal side thromboemboli warrants clinical evaluation for FVL in infant and potentially the parents.