Normal placentation

• Placental lakes are echolucent areas seen often in the centre of a cotyledon or between cotyledons
• The lakes may be quite large and are a common finding in normal pregnancies from the end of the first trimester
• Placental lakes arise due to a larger than average spiral vessel supplying an increased blood flow to the cotyledon
• The impact on the cotyledon is limited as usually only a single spiral artery is involved

The shape and number of lakes depend on:

• Gestational age
• Location of the placenta
• Pressure by the ultrasound probe