December 14, 2009

U/S about placenta


Very vascular – has 2 blood supplies

Blood from fetus through 2 (sometimes 1) umbilical arteries through umbilical cord from fetal hypogastric arteries to placenta

1 umbilical vein carries blood back to fetal left portal vein

Blood from mom through branches of uterine arteries through the myometrium (arcuate arteries) through the basilar plate (spiral arteries) into the placenta

The two circulations intertwine in the placenta but do not mix

Exchange of oxygen and nutrients occurs over the large vascular surface area

Maternal venous channels in the placenta are hypoechoic or anechoic spaces called venous lakes (usually small, but can be large)

Anatomy on US

Inner border of placenta against the uterine wall has the combined hypoechoic myometrium and interposed basilar layer = hypoechoic band called the decidua basalis (contains maternal blood vessels)

Outer surface abutting the amniotic fluid = chorionic plate (chorioamniotic membrane) = bright specular reflector

Placental thickness judged subjectively

But if measure at midposition or cord insertion 2-4 cm = normal

Grade 0

1.Late 1st trimester-early 2nd trimester

2.Uniform moderate echogenicity

3.Smooth chorionic plate without indentations

Grade 1

1.Mid 2nd trimester –early 3rd trimester (~18-29 wks)

2.Subtle indentations of chorionic plate

3.Small, diffuse calcifications (hyperechoic) randomly dispersed in placenta

Grade 2

1.Late 3rd trimester (~30 wks to delivery)

2.Larger indentations along chorionic plate

3.Larger calcifications in a “dot-dash” configuration along the basilar plate

Grade 3

1.39 wks – post dates

2.Complete indentations of chorionic plate through to the basilar plate creating “cotyledons” (portions of placenta separated by the indentations)

3.More irregular calcifications with significant shadowing

4.May signify placental dysmaturity which can cause IUGR

5.Associated with smoking, chronic hypertension, SLE, diabetes


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