Luteinizing Hormone (LH) is a glycoprotein hormone produced and released by cells in the anterior pituitary gland. LH regulates the reproductive system in both men and women. In men, LH stimulates the Leydig cells in the testes to produce testosterone, supporting sperm production and male characteristics. In women, LH is involved in ovarian function and the menstrual cycle.
LH’s Role in Ovulation
In women, LH plays a specific role in the menstrual cycle, particularly in triggering ovulation. Levels of LH are low for most of the monthly cycle. However, around the middle of the cycle, as a developing egg reaches a certain size, there is a significant increase in LH levels, known as the “LH surge.”
This LH surge signals the ovary that a mature egg is ready to be released from its follicle. Ovulation, the process of releasing a mature egg from the ovary, occurs about 24 to 36 hours after the LH surge begins. Ovulation predictor kits (OPKs) are designed to detect this surge in urine, helping individuals identify their most fertile window when trying to conceive.
LH Levels During Pregnancy
Once conception and implantation occur, the body’s hormonal focus shifts from ovulation to maintaining the pregnancy. During this period, LH levels decrease significantly, often falling to less than 1.5 IU/L, and remain low and stable throughout gestation. This reduction in LH allows other hormones, such as human chorionic gonadotropin (hCG), progesterone, and estrogen, to become dominant.
These hormones work together to maintain the uterine lining, support the developing embryo, and prepare the body for the changes of pregnancy. While LH plays a role in supporting the corpus luteum in the very early stages to produce progesterone, once the placenta takes over hormone production around 10-12 weeks, LH is no longer needed at elevated levels. Therefore, LH is not considered a primary indicator for confirming pregnancy.
Understanding Ovulation Tests and Pregnancy
A common point of confusion arises when individuals use ovulation predictor kits (OPKs) during early pregnancy, sometimes leading to a positive result. However, the pregnancy hormone, human chorionic gonadotropin (hCG), shares a similar chemical structure with LH.
Because of this structural similarity, an OPK may sometimes detect hCG and show a positive result, even when ovulation is not occurring. OPKs are not designed to confirm pregnancy and are less sensitive than dedicated pregnancy tests. A positive OPK during suspected pregnancy does not definitively mean pregnancy; a proper pregnancy test, which specifically detects hCG, is the only reliable way to confirm pregnancy.