According to the World Health Organization (WHO), third trimester intrauterine fetal death (TT-IUFD) is considered the birth of a child showing no signs of life that occurs from the 28th week of pregnancy onwards, whereas many differences can be found between different states (http://www.who.int/maternal_child_adolescent/epidemiology/stillbirth/en/). In Italy, specifically in Emilia Romagna Region, TT-IUFD is defined as the loss of a fetus at a gestational age of at least 22 weeks. When the gestational age is not known or not calculable, a stillborn with a birth weight of 500 gr or a length of 25 cm is classified as TT-IUFD .
The difficulties encountered in the diagnosis and international classification of intrauterine death are influenced by the multiplicity of possible causes and factors related to fetal death .
According to the Lancet Ending Preventable Stillbirths study group, late gestation stillbirth rates vary across high-income countries from 1.3 to 8.8/1000 births. However, these results may further be reduced with correct analysis of risk factors (obesity, advanced maternal age, in vitro fertilization), access to antenatal healthcare, accurate monitoring during pregnancy, improved data from stillbirth autopsies performed by a trained perinatal pathologist, and optimizing bereavement care .
Regardless of definitions and statistics, there are several reasons why it is important to deal with TT-IUFD. Stillbirth is still an unknown phenomenon, not allowing appropriate interventions to prevent and reduce its frequency. Problems related to the frequent lack of consent to autopsy, or to the absence of fetal and/or placenta examination, reduce the possibility to identify the cause of death.
Understanding the reasons for the event is important either for the relationship between doctor and patient, or for the care planning of future pregnancies. This may ensure adequate support for mothers and family members .
Furthermore, the lack of information on TT-IUFD leads to the high frequency of medico-legal litigation, which, besides representing a very long-lasting drama for family members and for the doctor, raises overall healthcare costs. Currently, also in Italy, obstetric practice has an increasing number of medico-legal implications. Moreover, the reduced number of births results in a great expectation towards pregnancy and its outcome. The increased average age of pregnant women raises risk factors, which can inevitably lead to an enhancement in TT-IUFD incidence.
Maternal risk factors for TT-IUFD are diabetes, obesity, hypertension, and thrombophilia. A high number of pregnancies resulting in a TT-IUFD do not present maternal risk factors and lead therefore to medico-legal disputes. In these cases, it is of paramount importance to dispose of useful elements to diagnose the fetus-placental suffering and its time of onset, in order to verify if there has been a delay in the gynecological intervention. A useful aid in this sense is given by the estimated age of any present thrombi that, together with other data, help timing the fetus-placental suffering.
Placental anomalies are the most common cause of TT-IUFD (more than 60%); however, a good percentage (about 25%) still occurs due to unknown causes . From a review made by Ptaceck et al. , more than 30% of TT-IUFD are due to placental abnormalities such as abruption, infarction, chorioamnionitis, villous dysmaturity, HEV, insufficiency, perivillous fibrin deposits, placental chorangioma, retroplacental hematoma, feto-maternal hemorrhage, placenta praevia, cord accident, and hydrops. Nevertheless, the precise role of placental lesions in fetal mortality remains uncertain, and the determination of causality in a single case is difficult especially when no maternal risk factors are known. This is due to differences in diagnostic criteria and in classification of clinical information.
Vascular lesions, especially thrombosis, are the second most common cause of fetal damage in the last weeks of pregnancy, including death . The umbilical cord thrombosis has an incidence from 1 to 10 in the stillbirths . It is usually linked to villous dysmaturity or cord anatomical anomalies (hyper- or hypocoiling, restriction, anomalous insertions in the placenta), as well as compression, torsion, or entanglement around fetal parts and true knots.
An organized thrombus may indicate a long-lasting fetal suffering, while fresh thrombi, dated less than few hours, usually may indicate an acute fetal suffering. This may lead to different medico-legal scenarios.
In literature, there are very few studies concerning the timing of thrombi. Irniger et al.  and Fineschi et al.  propose classifications of the histological age of thromboses and embolisms. Both studies refer, besides erythrocytes, platelets, and fibrin, an immediate presence of white blood cells up to the third day, when white blood cells become pyknotic and monocyte increase in number with enlarged nuclei. In the Irniger’s study starting from day 4th (phase III: 4th–20th day), the first capillaries are seen together with fibroblasts, mesenchymal cells, and hemosiderin-accumulating histiocytes. In Fineschi’s study, calcium, as precipitates with von Kossa stain, is seen within the first week, while fibroblasts’ penetration is seen from the 2nd week. Calcium precipitation is due to the action of the phosphatases released following the cell lysis that precipitates the calcium salts.
A more detailed timing of thrombi formation and characterization is available on mouse model by Nosaka et al. [11, 12].
Unfortunately, until now, studies on human thrombi never focused on a reliable marker of chronology, and all information refer to large timeframes of days or weeks. In medico-legal litigation cases, the timing of events can be of crucial importance, and, for what concern thrombi, especially the first hours or days .
Starting from the general agreement that white cells are immediately predominant in very early thrombi, and with time the number of monocytes increases, in the present study, the ratio between neutrophiles and macrophages is investigated and related to the timing of thrombi of placental and umbilical cord human samples. Besides, according to the main characteristics of the thrombogenesis and its evolution, the presence of fibroblasts and neovascularization as well as hemosiderin and calcium precipitates staining were evaluated.