The thecal sac is a part of the ovarian follicle that plays a crucial role in hormone production and ovulation. It is composed of specialized cells called thecal cells, which produce androgens (hormones that play a role in the development of male characteristics). During the menstrual cycle, under the influence of the luteinizing hormone (LH), the thecal sac undergoes changes that are essential for ovulation.
Prior to ovulation, the thecal sac surrounding the fully mature follicle expands and becomes thin, leading to its eventual rupture. This process is triggered by the surge in LH levels, commonly known as the LH surge. As the thecal sac effaces or thins out significantly, the follicle wall weakens, and the pressure within the follicle increases. This increased intra-follicular pressure eventually causes the follicle to rupture, leading to the release of the egg (ovulation).
Complete effacement of the thecal sac is one of the key events indicating imminent ovulation. It can be monitored through ultrasound examinations, where the appearance of a thin or barely visible thecal sac is considered a sign of impending ovulation. Identifying this stage of follicular development is particularly important for individuals undergoing fertility treatments, such as in vitro fertilization (IVF), where precise timing is necessary for optimal success.