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Placental maturity refers to the degree of structural and functional maturation of the placenta during pregnancy, as assessed primarily by ultrasound (USG). It reflects calcification, echotexture, and contour changes that occur as gestation advances, providing an indirect indicator of placental aging and uteroplacental function.
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The grading of placental maturity is classically described by Grannum’s classification (Grades 0–III), based on sonographic appearance of calcifications, chorionic plate contour, and basal echogenicity.
The placenta and placental bed in the first trimester: The chorionic plate is on the fetal side of the intervillous space. From the chorionic plate projects the villous placenta, which comprises a mesenchymal core surrounded by villous trophoblast (outer layer, syncytiotrophoblast; inner layer, cytotrophoblast). The villous placenta includes stem villi adjacent to the chorionic plate, floating villi and anchoring villi towards the maternal side. At the anchoring villus, a column of cytotrophoblast anchors the placenta into the decidual placental bed. The decidua is the endometrium of pregnancy, containing decidual (resident stromal) and inflammatory cells, veins, spiral arteries and secretory glands. These maternal glands secrete glucose and glycoproteins into the intervillous space. Spiral arteries are plugged with the cytotrophoblast and undergo upstream mural conversion with eventual loss of spirality. The surface of the placental bed in early pregnancy is covered with a cytotrophoblast shell. The myometrium is the subjacent muscle layer through which the spiral arteries pass.
Aplin, J.D., Myers, J.E., Timms, K. et al. Tracking placental development in health and disease. Nat Rev Endocrinol 16, 479–494 (2020). https://doi.org/10.1038/s41574-020-0372-6
The near-term placenta and placental bed with spiral arterial pathology: In normal near-term pregnancy, converted spiral arteries that are free of cytotrophoblast plugs transport blood into the intervillous space. Note the decidual arterial segment has now lost its original spiral shape. Venous drainage (right) enables transport of waste products away from the placenta. Failure of spiral artery conversion could result in damage to the villous syncytiotrophoblast caused by turbulent blood flow, which results from stenosis in the myometrial segment of a spiral artery that has not been fully transformed. Adaptation in the arterial supply could potentially be impaired further upstream. Pathophysiology of vessels in the chorionic plate that transport the transferred oxygen and nutrients to the fetus can also contribute to fetal growth restriction.
Aplin, J.D., Myers, J.E., Timms, K. et al. Tracking placental development in health and disease. Nat Rev Endocrinol 16, 479–494 (2020). https://doi.org/10.1038/s41574-020-0372-6
| Grade | Gestational Age | Ultrasound Features | Clinical Relevance |
|---|---|---|---|
| 0 | ≤18 weeks | Homogeneous; smooth chorionic plate | Normal early stage |
| I | 18–29 weeks | Mild undulations; few calcifications | Normal mid-pregnancy |
| II | 30–38 weeks | Basal calcifications; lobulated; indentations not reaching basal plate | Normal late stage |
| III | ≥ 38 weeks (term) | Extensive calcifications; cotyledons; indentations reach basal plate | Term or placental aging; premature in IUGR / preeclampsia |
B-mode ultrasound (BUS) and color Doppler energy (CDE) images for PMG, from left to right: grade 0, 1, 2 and 3; from top to bottom
Lei, B., Jiang, F., Zhou, F. et al. Hybrid descriptor for placental maturity grading. Multimed Tools Appl 79, 21223–21239 (2020). https://doi.org/10.1007/s11042-019-08489-x
Placenta appears more mature than expected for gestational age.