Introduction:
A placenta is a temporary vital organ formed during pregnancy to aid the fetus. The placenta adjusts its morphology, function, and growth according to the availability of oxygen and nutrients. In the case of a hypoxic environment, as an adaptive response, the placenta adjusts and increases its maturation rate. An accelerated maturation decreases the branching of villous and certain aspects of age-related parenchymal damage, which is usually less frequent in preterms, such as increased syncytial knots and the increased presence of fibrin (protein formed during blood clotting).
A suddenly increased maturation is a sign of maternal vascular malperfusion (MVM). A maternal vascular malperfusion (MVM) of a placenta denotes a specific pattern of placental injury that is related to an altered intervillous and uterine blood flow. MVM reflects an abnormal remodeling of the spinal artery causing abnormalities in the oxygenation process and disrupting the intervillous space flow dynamics. MVM is often associated with a condition called preeclampsia.
What Is a Hypermature Placenta?
A hypermature placenta is distinguished by its predominant terminal villi (functional unit that transfers nutrients and electrolytes between the fetus and the mother) and increased syncytial knotting (multinucleated collection of syncytial nuclei at the surface of terminal villi in the placenta). A hypermature placenta is when the placental maturity index obtained from the normotensive pregnancy placentas is above the 90th percentile.
What Are the Types of Hypermature Placenta?
Placental prematurity can be heterogeneous prematurity or homogenous prematurity. In heterogeneous prematurity, the preterm placenta (early placenta) has the same morphology as a term placenta. In contrast, homogenous prematurity is considered abnormal despite its gestational age.
What Causes Placental Maturity?
Placental maturity is related to maternal factors like age, gestational age, anemia, and smoking habits.
In What Conditions Is Placenta Considered Hypermature?
-
Preeclampsia - Hypertensive disorders during pregnancy increase placental maturity (hypermature placenta). Placental prematurity is linked with an early gestational age in pregnant women with preeclampsia. It was not noted in a normotensive group. In the placentas of women with preeclampsia, higher proportions of infarct areas were noted more than in normotensive (having normal blood pressure) pregnant women. The presence of an infarct is a continuation of a few changes to pathological and extensive involvement. Placental insufficiency can develop if they are thick, randomly distributed, centrally located, and numerous.
-
Some of the other pathological findings seen in the placenta of hypertensive diseases during the pregnancy include infarctions in placental villi, absence of villi regardless of the stage of development, inflammation, lesions of the uteroplacental malperfusion like increased perilous fibrin, decidual vasculopathy, and chronic deciduitis. Some ischemic changes include increased syncytial knots, accelerated villous maturation, hypovascularity, and agglutination. At the microscopic level, focal necrosis of syncytiotrophoblast occurs along with the distortion and loss of microvilli, and hyperplasia may be present around cytotrophoblastic cells with apoptosis or degeneration of other cells.
-
Avascular villi and villitis are more seen in preeclampsia. The angiogenesis and placental vascularization are relatively poor in a scenario with an increased hypertensive level. The placental maturity index and the hypermaturity of the placenta are increased in pregnant women with preeclampsia but not in pregnant women with gestational hypertension.
-
Preeclampsia Small for Gestational Age (SGA) Newborns - Newborns are classified as small for gestational age (SGA), adequate for gestational age (AGA), or large for gestational age (LGA). Placentas of newborns that are small for gestational age (SGA) were more likely to be hypermature placenta than placentas of newborns with appropriate gestational age (AGA).
-
Low Birth Weight - Hypermature placenta is related to low birth weight. Hypermature placenta in pregnant women with preeclampsia shows an intrauterine growth restriction (IUGR) resulting in low birth weight in gestational age. It was also noted in preterm pregnancies than in term pregnancies.
-
Smoking - Hypermature placenta was more noted in pregnant women who smoke than in ones who do not. Using a portion of syncytial knots as a placental maturity marker, the placentas of women who smoke were found to have premature aging and degenerative changes.
How Does a Hypermature Placenta Cause Preeclampsia?
Placental ischemia is caused by an incomplete remodeling of the spiral arteries of the uterus due to an inadequate invasion of the trophoblast. Necrosis of villous tissue results from ischemia. The hypoxic and poorly perfused placenta is released. It synthesizes an increased amount of a few vasoactive factors like cytokines, angiotensin II (ANGII) type 1 receptor autoantibodies (ATI-AA), and soluble fms-like tyrosine kinase-1 (sFlt-1). These vasoactive factors induce widespread dysfunction or activation of maternal endothelium of other organs and kidney vessels, ultimately resulting in hypertension.
In addition, the ischemic placenta alters the balance of the circulating levels of antiangiogenic or angiogenic factors like placental growth factor, sFlt-1, and vascular endothelial growth factors leading to an endothelial cell dysfunction of the maternal vasculature. All these factors, mainly the sFlt-1 levels, play a vital role in the initiation of symptoms of preeclampsia.
How Are Hypermature Placentas Assessed?
Placental Maturity Index: Hypermature placenta is assessed histologically by the placental maturity index. The placental maturity index is related to birth weight and gestational age and measures the thickness of epithelial plates in the terminal villi and their number. Both these measures are straightaway related to placental maturity. Usually, the placental maturity index is always noted to be higher in pregnant preeclamptic women than in normotensive pregnant women in their preterm and not at-term pregnancies.
Hypermaturity of the Placenta: Hypermaturity of the placenta is also used to diagnose newborns' SGA.
Placental Grading: The maturity of a placenta is graded using an ultrasound grading system. Grading is mainly based on the visual appearance of the placenta. The changes occurring to the placental substance, chorionic plate, basal layer, and the different grades of the grading system are given below:
1. Grade 0: Late first to early second trimester (less than 18 weeks).
-
Placental Substance: In grade 0, the placental substance does not contain any echogenic areas and has an echotexture that is uniform and homogenous.
-
Basal Layer: No echogenicities are noted in the basal layer.
-
Chorionic Plate: The chorionic plate has an unbroken, well-defined dense line, which is also smooth and straight.
2. Grade 1: Grade 1 is the earliest ultrasound change noted in the maturation of the placenta (18 to 29 weeks).
-
Placental Substance: In grade 1, loss of homogeneity occurs in the placenta due to the appearance of a few scattered echogenic areas. In addition, occasional parenchymal calcification is noted.
-
Basal Layer: Here, no echogenicities were noted in the basal layer.
-
Chorionic Plate: Fine subtle undulation is present with an unbroken yet well-defined line.
3. Grade 2: Notable changes occur in all three layers during this stage (30 to 38 weeks).
-
Placental Substance: Due to the appearance of a comma-type density, the placental substance is divided incompletely.
-
Basal Layer: Occasional hyperechoic or calcification areas are noted in the basal layer. The long axis of the hyperechoic area is arranged parallel to the basal layer, and calcifications occur in a dot-dash configuration in the basal layer.
-
Chorionic Plate: Deeper indentations are noted here but do not reach the basal layer.
4. Grade 3: This is the last phase representing a mature placenta (more than or equal to 39 weeks). An early progression to a Grade 3 placenta is associated with placental insufficiency and leads to a hypermature placenta.
-
Placental Substance: The placenta gets divided into various compartments demarcating the cotyledons. The central area of these compartments shows a fallout or echo-spared area.
-
Basal Layer: Significant basal plate calcification is noted, and the echogenic densities become larger, denser, and persist longer.
-
Chorionic Plate: Here, the indentations of the chorionic plate extend up to the basal layer and represent the cotyledon.
Conclusion:
The placental hypermaturity is mainly related to maternal factors like anemia and smoking. However, it can also be seen in conditions like preeclampsia and SGA newborns. Although an increased placental maturation or hypermature placenta is a sign of placental pathology, it is more considered a sign of uteroplacental insufficiency leading to a counteractive and adaptive mechanism.
