Gebet means area as you probably know, but I think what's meant here is placental tissue or placenta on its own should be OK too.
"Thrombosis
Blood clots forming in the placenta or uterus may lead to loss of the fetus. This is an unusual circumstance, but may occur in patients who carry a clotting tendency, or thrombophilia (a propensity for developing clots). If a pregnancy is lost in the second trimester, the placenta should be sent for analysis. If blood clots or evidence of poor blood flow is found in the tissue, then the patient may want to consider using a blood thinner such as heparin in future pregnancies."

... thrombosis in the placental bed ...
www.ncbi.nlm.nih.gov/pubmed/9653861

There is thrombosis seen as low signal intensity on T2 weighted ... blood flow as a consequence of a vascular defect in the placental bed
fn.bmj.com/content/early/2011/08/17/adc.2010.196451.full

This may account for the formation of microthrombi in the terminal capillary system in the placental bed of preeclamptic pregnancies.
books.google.com/books?isbn=078173066X...

the authors speculated that factor V Leiden-induced thrombosis in the placental bed with subsequent hypoxia ...
www.clinchem.org/content/49/7/1081.full

All these conditions are associated with thrombotic damage in the placental bed.
linkinghub.elsevier.com/retrieve/pii/S1751721409001791