Luteal phase progesterone deficiency may or may not be a contributing factor to miscarriage. In the luteal phase, estradiol, in conjunction with progesterone, prepares the endometrium for implantation. Actions of estradiol are required before the exposure of progesterone in the luteal phase. Food intake increases by approximately 10% during the luteal phase compared to the follicular phase. In women with PMS, food intake is higher in the luteal phase than follicular. Small luteal cells have LH receptors that regulate PKA activity within the cell. Theca lutein cells are also known as small luteal cells. Cholesterol-LDL complexes bind to receptors on the plasma membrane of luteal cells and are internalized. However, many women have shorter luteal phases, and a few have longer luteal phases. The issue of a luteal phase defect is complex.