Luteinizing Hormone (LH) is a gonadotropin, a hormone produced by the pituitary gland in the brain that plays a direct role in reproduction. In the natural menstrual cycle, LH works with Follicle-Stimulating Hormone (FSH) to promote the growth and maturation of an egg within a fluid-filled sac called a follicle. The LH level is carefully monitored throughout the In Vitro Fertilization (IVF) process, particularly during the ovarian stimulation phase before egg retrieval. This monitoring ensures that the developing eggs are captured at the optimal time, just before the body’s natural processes would release them. Careful control of LH levels is central to the success of an IVF cycle, preventing the loss of mature eggs.
The Role of LH in the IVF Cycle
In a natural cycle, a rapid, massive spike in LH, known as the LH surge, signals the ovary to release the mature egg (ovulation). This surge typically occurs 24 to 36 hours before the egg is released. The goal of the ovarian stimulation phase in IVF is to grow multiple follicles simultaneously, maximizing the number of eggs available for retrieval.
The primary risk during stimulation is a “premature LH surge,” where the body attempts to ovulate before the eggs can be collected. If this uncontrolled surge occurs, the eggs would be spontaneously released, and the cycle would need to be canceled. Therefore, the strategy for most IVF protocols is to administer medications that suppress the pituitary gland, preventing the brain from sending the LH surge signal prematurely. This allows the fertility specialist to control the exact timing of final egg maturation and collection.
Target LH Levels for Successful Retrieval
The target LH level during the ovarian stimulation phase, leading up to the trigger shot, is one of active suppression. The goal is to maintain LH at a low, basal level to prevent a spontaneous, premature surge and ovulation. While specific thresholds vary between clinics, LH levels are generally desired to be below 10 mIU/mL during stimulation.
Some studies suggest maintaining the LH level below 5 mIU/mL is optimal, with certain protocols aiming for levels as low as 1.2 mIU/L after suppression medication begins. An LH level rising above 10 mIU/mL is a clinical marker for a premature surge, which can lead to premature luteinization of the follicles. Luteinization is the process where the follicle converts into a corpus luteum, potentially causing the egg to become over-mature or spontaneously release before retrieval. Maintaining suppressed levels ensures the maximum number of eggs are retained within the follicles until the final trigger shot is administered.
Protocols Used to Control LH
Two main types of protocols are used to achieve the necessary suppression of LH and prevent the premature surge: the Gonadotropin-Releasing Hormone (GnRH) Antagonist protocol and the GnRH Agonist protocol. These medications act on the pituitary gland, which is the body’s control center for LH release. The Antagonist protocol is often favored for its shorter duration and simpler administration schedule.
The GnRH Antagonist protocol, using medications like Ganirelix or Cetrorelix, immediately blocks receptors on the pituitary gland. This direct blockage prevents the pituitary from responding to brain signals, suppressing LH release within hours. Antagonists are typically started midway through the stimulation cycle, after follicles have begun growing, and are continued until the trigger shot.
In contrast, the GnRH Agonist protocol, often called the “long protocol,” uses medications like Lupron. Agonists initially cause a temporary “flare-up” of LH and FSH release from the pituitary gland. However, continuous administration over several days exhausts and desensitizes the pituitary receptors, leading to profound suppression of LH and FSH.
This down-regulation takes longer, usually starting in the cycle preceding stimulation, but provides a stable, suppressed hormonal environment throughout the follicle growth phase. Both protocols are highly effective in controlling LH, achieving this control through different mechanisms and timing.
The Timing of the Trigger Shot and Final Monitoring
Once follicles reach the appropriate size (typically 17 to 20 millimeters in diameter), the focus shifts from suppressing LH to actively mimicking its surge. The final step before egg retrieval is the administration of the trigger shot, a precisely timed dose of Human Chorionic Gonadotropin (hCG) or a GnRH agonist. The hCG molecule is chemically similar to LH and binds to the same receptors, acting as an artificial, powerful LH surge.
This artificial surge initiates the final maturation process within the eggs, preparing them for collection. Since the trigger shot creates a massive, controlled surge, LH monitoring becomes irrelevant immediately after the injection. The egg retrieval procedure is scheduled for a specific window, usually 34 to 36 hours after the trigger injection. This timeframe is necessary to collect the eggs when they are fully mature but before the artificial surge causes spontaneous ovulation.