Placental Lakes on Sono: Implications?

This episode subject was requested by Emily, one of our podcast family members. She has noticed the reporting of “large placental, venous lakes” on antepartum ultrasound. Placental lakes are enlarged spaces in the placenta filled with maternal blood. These spaces are also called intervillous spaces because they are found between the placental villi the finger-like projections of the placenta that contain fetal blood vessels . The placental villi float in the intervillous spaces and absorb oxygen and nutrients from the maternal blood. The blood-filled placental lakes appear nearly black on ultrasound because they do not reflect soundwaves back to the ultrasound machine. Placental lakes can be seen within the placenta or on the fetal surface of the placenta bulging into the amniotic cavity. Slow swirling blood flow may be seen within the spaces, and the shape of the spaces tends to change with uterine contractions. These features may help to distinguish a placental lake from a thrombus. Well, why is this even supposed to be an issue? How can venous lakes affect the fetus, after all…maternal blood is normally found in the intervilluous spaces between the chorionic villi which house the placental vessels for gas exchange. Well, the theory is that these large placental lakes may affect blood redistribution in the chorionic fetal vessels, leading to increased incidence of placental growth abnormalities or fetal distress in labor. Are these placental sono findings a harbinger of bad things to come or are they simply benign findings? Let’s look at the data!