An examination of the maternal vascular response to placentation shows that physiological changes in the placental bed normally extend from the decidua into the inner myometrium. In pre-eclampsia and in a proportion of pregnancies with small-for-gestational age infants (SGA) the physiological changes are restricted to the decidual segments alone. In addition, complete absence of physiological changes throughout the entire length of some spiral arteries is seen in pre-eclampsia and SGA. This new observation is confirmed in a study of basal plates of placentas from abnormal pregnancies. Intraluminal endovascular trophoblast may be seen in the placental bed spiral arteries in the third trimester in pre-eclampsia and SGA, a feature not seen beyond the second trimester in normal pregnancy. These findings point to a defect in the normal interaction between migratory trophoblast and maternal uterine tissues in pre-eclampsia and in SGA.

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The incidence of placenta accreta, defined as the abnormal adherence of the placenta to the uterine wall, has been increasing alarmingly in the developed as well as the developing world. There is considerable maternal morbidity and mortality related to the condition. The pathophysiology focuses on the balance between decidualisation on the one hand and trophoblast invasion on the other. Pathological diagnosis relies on the finding of placental villi in direct apposition to myometrium, either in hysterectomy specimens or in placental basal plates.

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The terminology and diagnostic criteria presently used by pathologists to report invasive placentation is inconsistent and does not reflect current knowledge of the pathogenesis of the disease or the needs of the clinical care team. A consensus panel was convened to recommend terminology and reporting elements unified across the spectrum of PAS specimens (i.e. delivered placenta, total or partial hysterectomy with or without extrauterine tissues, curetting for retained products of conception). The proposed nomenclature under the umbrella diagnosis of Placenta Accreta Spectrum (PAS) replaces the traditional categorical terminology (placenta accreta, increta, percreta) with a descriptive grading system that parallels the guidelines endorsed by the International Federation of Gynaecology and Obstetrics (FIGO). In addition, the nomenclature for hysterectomy specimens is separated from that for delivered placentas. The goal for each element in the system of nomenclature was to provide diagnostic criteria and guidelines for expected use in clinical practice.

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In consenting to a perinatal autopsy, the primary motive of parents may be to find the exact cause of death. A critical review on the value of perinatal autopsies was performed to see whether parents could be counseled regarding their main motive. A literature search was performed in MEDLINE, EXCERPTA MEDICA, and the Cochrane library. We evaluated the value of the autopsy by comparing the clinical and autopsy diagnoses in stillbirths, neonatal deaths, and therapeutic terminations. Clinicopathologic concordance was divided into four categories: (1) change in diagnosis, (2) additional findings, (3) complete confirmation, and (4) inconclusive. We sought information on factors that may influence the value of perinatal autopsies: the type and definitions of perinatal loss; autopsy rate; level of hospital; expertise of pathologists; autopsy protocol used; whether patients were inborn or referred; and antenatal diagnosis. From the 27 articles that met our review criteria, the autopsy revealed a change in diagnosis or additional findings in 22% to 76% of cases. If confirmation of clinical findings is included, then the value of the perinatal autopsy was as high as up to 100%. Factors that could influence this rate were reported variably by investigators. When centers report their experience of the value of the perinatal autopsy, information on the factors that may influence their reports should be provided as well. Clinicians can confidently advise parents of the usefulness of the perinatal autopsy in ascertaining the cause of death or for counseling their future pregnancies.