HCG Trigger (Human Chorionic Gonadotropin Trigger)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 14, 2026

An hCG trigger is an injectable dose of human chorionic gonadotropin given during a monitored cycle to induce final follicular maturation and ovulation by mimicking the body's natural LH surge. The trigger works because hCG is structurally similar to LH and binds the same receptor, producing the hormonal signal needed for the dominant follicle to complete maturation and rupture.¹ Timing of the injection is guided by follicle development monitoring, typically via ultrasound assessment of follicular size alongside cycle observation data.

The hCG trigger is used across several clinical contexts. In assisted reproductive technology, including IVF and IUI, it serves to synchronize oocyte maturation with the procedure schedule, functioning as a component of the stimulation protocol rather than a therapeutic intervention in its own right.² These contexts differ fundamentally in purpose from restorative use. In ART, the trigger times a retrieval or insemination. In restorative care, the goal remains conception within the body. The two applications share a pharmacological mechanism but not a clinical paradigm.

Named methods in restorative reproductive medicine, including NaProTechnology, use hCG selectively for documented ovulatory dysfunction: a delayed or absent endogenous LH surge, inadequate follicular response, or timing variability that makes natural intercourse less precise.³ Some NaProTechnology protocols also use post-ovulatory hCG to support corpus luteum function in the early luteal phase.³¹ Decisions about whether to use an hCG trigger, and when in the cycle to administer it, are made by the treating physician based on cycle chart data, ultrasound findings, and individual history. The treating clinician determines protocol design and timing; no standardized dose schedule applies uniformly across named methods or individual patients.

The hCG trigger should be distinguished from follicle stimulation agents such as clomiphene and letrozole, which act earlier in the cycle to promote follicular growth. The trigger does not stimulate follicle development; it signals a mature follicle to complete ovulation. In practice, the two interventions are often used sequentially in the same cycle: stimulation first, triggering when monitoring confirms follicular readiness.¹ and luteal phase.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.