[Dynsei]

You may be on to something about high estrogen levels. Luteal swelling could be caused by either three of either prolactin, progesterone, or estrogen which either can be naturally high during the luteal phase. Estrogen might be responsible for ending the luteal phase. Prolactin reduces estrogen, and it allows the luteal phase to stay longer. The egg releases progesterone, which prolactin allows it to stay longer. Prolactin is compatible with progesterone. Estrogen is usually present, but doesn't have to be high for this stage. Estrogen is instead needed to signal the start of the luteal phase.