YOUR MENSTRUAL CYCLE TIMELINE
Cycle Day 1 (actually just before): The body gets the signal that no conception has occurred. Hormones drop, which signal the onset of shedding the menstrual lining, your period.
Cycle Days 2-3 up to Ovulation: The pituitary gland of the brain releases Follicular Stimulating Hormone (FSH) to grow a cohort of follicles in the ovary, with one expected to take the lead to ovulate an egg. As follicles grow, they secrete Estrogen, which signals the uterine lining to grow and ultimately changes the form of cervical secretions to allow passage of sperm to egg.
Cycle Day 14 +/-: Follicles have grown from their original size of 3-4mm, and a dominant follicle has reached approximately 20mm. The concurrent rise in estrogen as these follicles grow trigger the pituitary gland to release another hormone called Luteinizing Hormone, (LH) which triggers ovulation within 12-24 hours. This is the hormone that many Ovulation Predictor Kits use to measure the levels of LH in urine.
Cycle Day 17+/-21: Once the egg is released from the follicle, the follicle transforms itself to the Corpus Luteum and begins to secrete Progesterone, which helps to thicken the endometrial uterine lining for embryo implantation. If conception occurs, the fertilized egg travels from the fallopian tube and in 5-6 days travels to the uterus to begin implantation. The embryonic cells attach to the uterine lining and release human gonadotropin hormone (hCG), the hormone that signals pregnancy is underway.
Cycle Day 28+/-: If no conception occurs, no hCG is released and all hormone levels drop so that the endometrial menstrual lining sheds and the process begins anew.