The Luteal Phase is the second phase of the menstrual cycle, which begins after ovulation.
In the luteal phase, the follicle that released the egg becomes a structure called the corpus luteum. The corpus luteum secretes progesterone, which causes the uterine lining to thicken to prepare for a fertilized egg.
Progesterone secreted at this stage leads to vaginal discharge that is thicker and stickier, even dry. Progesterone also raises body temperature and affects the cervix, which gets lower, firmer, and more closed. This creates a hostile environment for sperm. The continued release of progesterone and—to a lesser extent—estrogen (also produced in smaller amounts by the corpus luteum) also maintains the uterine lining and inhibits the release of FSH and LH.
Progesterone is responsible for some symptoms associated with premenstrual syndrome (PMS) such as bloating or fatigue. Testosterone levels also decline, which may lead to a dip in libido.
During this phase, the uterine lining develops to become a hospitable environment for a fertilized egg to attach, grow, and develop. If the egg is fertilized and the embryo implants in the uterus, the corpus luteum continues secreting hormones to support the pregnancy until the placenta takes over this function near the end of the first trimester.
If the egg is not fertilized, then after about ten to fourteen days, the corpus luteum starts to break down, ceasing production of progesterone. This disrupts the maintenance of the uterine lining, and causes it to shed, an average of fourteen days after ovulation. At this point, menstruation begins and a woman re-enters the follicular phase of her cycle
Niddah often begins with the onset of menstruation. Some women may experience light staining for a few days prior to the flow starting, as the uterine lining becomes less stable but hasn’t fully started shedding. Such staining does not necessarily make a woman niddah. Learn more about the laws of stains here. For discussion of a possible effect on veset calculations when this happens with regularity, see here.
