What is the primary effect of luteinising hormone (LH) in females?

Luteinising hormone (LH) plays a crucial role in the female reproductive system, particularly in the regulation of the menstrual cycle and ovulation. One of its primary effects is to trigger the process of ovulation, which involves the rupture of the mature follicle. This is when an ovum is released from the ovary, a key event for female fertility.

During the menstrual cycle, a surge in LH levels typically occurs around the midpoint of the cycle, leading to the release of the egg. This surge is preceded by an increase in estrogen levels from developing follicles, which ultimately signals the pituitary gland to release LH. The rupture of the follicle not only allows the egg to be released but also transforms the remnants of the follicle into the corpus luteum, which produces hormones like progesterone necessary for supporting the early stages of pregnancy, should fertilization occur.

In contrast to this primary function, the other options refer to different hormonal effects or biological processes that do not directly pertain to luteinising hormone. The letdown of milk is influenced by hormones like oxytocin, metabolic processes are more broadly regulated by other hormones such as thyroid hormones, and maintaining pregnancy predominantly involves hormones like progesterone rather than LH alone. Thus, the