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This chapter reviews the features of defective physiological changes of the spiral arteries in the placental bed in association with preeclampsia and fetal growth restriction and the methodology of placental bed vascular studies. The incidence of acute atherosis ranges from 41% to 48% in a series examining placental bed biopsies, placental basal plates, and amniochorial membranes. The basal plate of a delivered placenta is highly insufficient for the study of spiral arteries as it does not even represent the whole thickness of the decidua. The total number of spiral artery openings in the placental bed for a normal pregnancy was estimated at 120 and for severe preeclampsia 72. Indeed, examination of large hysterectomy specimens with placenta in situ has shown that in severe cases of preeclampsia a small, central part of the placenta may contain spiral arteries with fully developed physiological changes.
The causes of stillbirth are varied. Stillbirth may be due to obstetric conditions such as premature labor, fetal abnormalities, infections, intrapartum complications, placental and cord factors, maternal conditions, or drugs. A significant number remain unexplained despite a full investigation [1,2]. The rate of stillbirth in the developed world over the last 20 years has remained much the same or declined very slightly at around three per 1000 births (>28 week gestational age) using international comparisons . This decline in stillbirths has not mirrored the decline in infant deaths, though this may be due to the fact that there are now more older mothers, more maternal obesity , and more assisted conceptions, each increasing the risk of stillbirth.
The proportion of stillbirths that are assigned to the various categories depends upon the depth of the investigation and the classification system used. The proportion that is unexplained can vary from around 15–20% with ReCoDe  and Perinatal Society of Australia and New Zealand (PSANZ) (e.g., WA data) , to 60% with some of the older classification systems. The number of unexplained stillbirths can be reduced considerably by the use of a category of growth restriction, using charts customized to the mother’s parameters and using fetal growth measures derived from ultrasound measures, all of which increase the recognition of a substantial number of growth-restricted fetuses . There are now a number of different classification systems with various benefits and drawbacks [7,8].
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