Luteinizing hormone (LH) is a chemical messenger produced by the pituitary gland, located at the base of the brain. This hormone regulates reproductive functions in both males and females. Understanding LH’s functions provides insight into the complex processes of the reproductive system.
LH’s Primary Function
In women, luteinizing hormone is involved in maintaining the menstrual cycle and supporting the initial stages of a potential pregnancy. During the early part of the menstrual cycle, LH contributes to the growth of ovarian follicles. A significant increase in LH levels, often referred to as the “LH surge,” typically occurs around the middle of the menstrual cycle, triggering ovulation. After the egg is released, LH helps transform the remaining follicle into the corpus luteum, which then produces progesterone, a hormone that prepares the uterine lining for implantation.
Hormonal Shifts in Early Pregnancy
Following conception and implantation, the body’s hormonal landscape changes, primarily due to the emergence of human chorionic gonadotropin (hCG). It is produced by the developing placenta after implantation. hCG maintains early pregnancy by signaling the corpus luteum to produce progesterone, which supports the uterine lining. The presence of hCG is also what over-the-counter pregnancy tests detect in urine, making it the primary marker for confirming pregnancy. As hCG levels rise, they begin to influence other reproductive hormones.
LH Levels Through Pregnancy
Once pregnancy is established and human chorionic gonadotropin (hCG) levels begin to rise, the body’s production of luteinizing hormone (LH) typically decreases, a natural consequence of hormonal shifts supporting pregnancy. The reason for this suppression is that hCG has a structural similarity to LH and can mimic some of its actions, particularly in stimulating the corpus luteum to produce progesterone. Because hCG takes over progesterone production, the pituitary gland reduces LH output, making high LH levels unnecessary during gestation. Consequently, LH levels generally remain suppressed throughout pregnancy. While very early fluctuations might occur before hCG is fully established, a sustained increase in LH is not a characteristic of pregnancy and is not used for its detection.
Reliable Pregnancy Detection
Accurately detecting pregnancy relies on measuring human chorionic gonadotropin (hCG) levels, not luteinizing hormone (LH). Home pregnancy tests identify hCG in urine, providing a convenient and early indication of pregnancy. For earlier or more precise confirmation, blood tests can detect hCG, often before it is detectable in urine. These tests are reliable because hCG is almost exclusively produced during pregnancy by the developing placenta. Relying on LH levels for pregnancy confirmation would be inaccurate, as LH’s primary role is in the menstrual cycle leading to ovulation, and its levels decrease once pregnancy is established.