The placenta stores calcium for the fetus. The degree of placental calcification has, therefore, been associated with maternal serum calcium levels. Hence, the increased incidence of placental calcifications in primiparas and in pregnant women on calcium supplementation. Calcification of the placenta is an acknowledged physiologic phenomenon associated with increasing gestational age.
At 40 weeks gestation, approximately 20% of placentas have extensive calcification (Grannum grade 3). The original report by Grannum and co-workers suggested a correlation between maturational placental changes and fetal lung maturity, as measured by the lecithin/sphingomyelin (L/S) ratio. However, subsequent investigators did not find a relationship between placental grade and the mean L/S ratio or phosphatidylglycerol concentration. Hyaline membrane disease has been reported in neonates with a grade 3 placenta delivered prematurely for a pregnancy complication. Both placental grade and fetal lung maturity are interrelated by the independent variable of gestational age. When matched for maternal age, gravidity and gestational age, advanced placental maturity is not associated with pregnancy – induced hypertension, reduced fetal growth, or fetal asphyxia. There is an increased deposition of calcium in the placenta of women with severe pre-eclampsia prior to term. However, the degree of placental calcification is due to the primary disease process (i.e., pre-eclampsia) that results in fetal growth restriction and a secondary reduction in the transfer of calcium to the fetus. Fox does not consider placental calcifications clinically significant.
Calcification of the placenta is a normal physiologic process that occurs with advancing gestational age. If irregular calcifications are present within a circumscribed mass, a placental tumor should be considered.
Grannum and co-workers incorporated the amount of calcium visualized sonographically into a placental grading system:
Placental grade and description grade 0 – easily delineated, relatively straight chorionic plate and a homogenous placental texture throughout.
grade 1 – undulating chorionic plate and scattered echogenic foci throughout the placenta.
grade 2 – the placental intervillous spaces are divided by comma-like echogenic densities that originate at the chorionic plate; there are small echogenic areas along the basal layer of the placenta.
grade 3 – echogenic indentations extend from the chorionic plate to the basal layer, dividing the placenta into discrete components.
Sonolucent areas may be present within each placental subdivision.
Irregular densities that cast an acoustic shadow may be present on the chorionic plate.
While interesting, this grading system has not been helpful clinically in the management of the individual cases.