placental site involution postpartum

Last edited 11/2019

The separation of the placenta occurs in the decidual layer. After delivery the placental site contracts to about 50% of its original area. The contraction and retraction of the placental site causes occlusion of the spiral arterioles and so is important in the prevention of postpartum haemorrhage. There is infiltration of the placental bed by inflammatory cells and this superficial layer is shed.

The uterine cavity is re-epithelialized, except for the placental bed, after about 10 days. Re-epithelization of the area of the placental bed does not occur until about 6 weeks post delivery. During the period of re-epithelization the trophoblast and decidua are shed as a uterine discharge termed lochia. In the first 2-3 days post delivery the lochia is blood stained. After this initial discharge the lochia becomes serous and pale and lasts for about 20 days. A thicker, more mucoid, discharge then may occur for a further 4-8 weeks.