How Chorionic Gonadotropin Triggers Ovulation in IVF
Chorionic gonadotropin, specifically human chorionic gonadotropin (hCG), mimics luteinizing hormone (LH) to induce final egg maturation and ovulation in fertility treatments like IVF. After ovarian stimulation with follicle-stimulating hormone (FSH) to grow multiple follicles, doctors inject hCG (typically 5,000–10,000 IU) 34–36 hours before egg retrieval. This surge prompts oocytes to resume meiosis and prepares eggs for fertilization.[1][2]
Why hCG Instead of Pure LH?
hCG has a longer half-life (24–36 hours) than native LH (about 20 minutes), providing sustained signaling for ovulation without needing multiple doses. Recombinant LH exists but is costlier and less common for triggers.[1][3]
Role in Timed Intercourse and IUI
For intrauterine insemination (IUI) or natural-cycle monitoring, hCG injections predict ovulation timing. Couples time intercourse or insemination 24–36 hours post-injection, boosting conception odds in unexplained infertility or mild male factor cases.[2]
hCG for Luteal Phase Support
Post-ovulation, low-dose hCG (1,500–5,000 IU every 3–7 days) supports the corpus luteum, maintaining progesterone production to sustain early pregnancy until placental takeover. It's an alternative to daily progesterone injections, though vaginal progesterone is now preferred due to lower ectopic pregnancy risk.1
Common Brands and Administration
Brands include Pregnyl, Novarel, Ovidrel (recombinant choriogonadotropin alfa), and compounded urinary hCG. Injections are subcutaneous or intramuscular; Ovidrel uses a prefilled pen for ease.[2]
Risks and Monitoring
Ovarian hyperstimulation syndrome (OHSS) risk rises with hCG, especially in high-responders—symptoms include bloating, nausea, and fluid shifts. Doctors monitor estradiol levels and follicle count pre-trigger, sometimes using GnRH agonists as "triggers" to reduce OHSS.3 Ectopic pregnancy rates may increase slightly with luteal hCG.[1]
Alternatives to hCG
GnRH agonist triggers (e.g., leuprolide) prevent spontaneous LH surges and lower OHSS risk but require intensive luteal support. Dual triggers combine low-dose hCG with GnRH agonists for balanced outcomes.[3]
[1]: https://www.asrm.org/globalassets/asrm/asrm-content/news-and-publications/practice-guidelines/for-non-members/ovarian-stimulation-in-ivf.pdf
[2]: https://www.ncbi.nlm.nih.gov/books/NBK562316/
[3]: https://www.fertstert.org/article/S0015-0282(19)32345-6/fulltext