What is the purpose of a trigger shot with In Vitro Fertilization (IVF)?

From the Guidelines

A trigger shot with IVF is typically administered 36 hours before egg retrieval, with human chorionic gonadotropin (hCG) being the most commonly used medication, at a dosage of 5000-10,000 IU, as recommended by recent guidelines 1. The trigger shot is a crucial step in the IVF process, as it induces final egg maturation and triggers ovulation. The medication and dosage used for the trigger shot are determined by the fertility doctor based on the patient's hormone levels and response to stimulation medications.

• The most commonly used medications for the trigger shot are:
  • Human chorionic gonadotropin (hCG) such as Pregnyl, Novarel, or Ovidrel
  • GnRH agonists like Lupron
• The trigger shot is typically injected subcutaneously (under the skin) in the abdomen, and the patient is required to abstain from food and drink for a specified period before egg retrieval.
• The timing of the trigger shot is critical, and it must be administered exactly when instructed, usually in the evening, to ensure successful egg retrieval.
• Some patients may experience mild side effects like injection site pain, bloating, or breast tenderness after the trigger shot.
• Recent studies have shown that the use of hCG for triggering ovulation is effective, and the timing of the trigger shot can be adjusted based on individual patient needs 1. The use of hCG at a dosage of 5000-10,000 IU is recommended, as it has been shown to be effective in inducing final egg maturation and triggering ovulation, with minimal side effects 1.

From the FDA Drug Label

In the absence of an endogenous LH surge, hCG is given when monitoring of the patient indicates that sufficient follicular development has occurred. This may be estimated by pelvic ultrasound alone or in combination with measurement of serum estradiol levels The combination of both pelvic ultrasound and serum estradiol measurement are useful for monitoring the development of follicles, for timing of the ovulatory trigger, as well as for detecting ovarian enlargement and minimizing the risk of the Ovarian Hyperstimulation Syndrome and multiple gestation

The trigger shot with IVF involves administering hCG when sufficient follicular development has occurred, as indicated by monitoring with pelvic ultrasound and/or serum estradiol measurement 2.

• The goal is to trigger ovulation and minimize the risk of Ovarian Hyperstimulation Syndrome and multiple gestation.
• The timing of the ovulatory trigger is crucial and is determined by the patient's response to treatment, as assessed by ultrasound and hormone levels.

From the Research

Trigger Shot with IVF

• The use of human chorionic gonadotropin (hCG) as a trigger shot in IVF has been evaluated in several studies 3, 4, 5.
• hCG trigger is associated with significant timing deviation from physiology, and peak progesterone is not synchronized with the implantation window 3.
• The luteal phase endocrinology post GnRH agonist trigger is characterized by a quick and irreversible luteolysis, and a freeze-all strategy is advised if there is a risk of ovarian hyperstimulation syndrome 3.
• A single 1,500 IU hCG dose, administered 48 h post oocyte retrieval, may be all that is needed to fully support the luteal phase and secure the best chances of achieving pregnancy 3.
• The addition of low-dose hCG to human menopausal gonadotropin (HMG) throughout the early follicular phase in controlled ovarian stimulation (COS) has been shown to improve pregnancy rates in some studies 4.
• The timing of hCG administration in IVF/ICSI protocols using GnRH agonist or antagonists has been evaluated, and delaying hCG administration may increase estradiol and progesterone levels and oocyte retrieval, but does not influence ongoing pregnancy rate per oocyte pick-up, miscarriage rate, and live birth rate 5.

hCG Biological Functions and Clinical Applications

• hCG is produced primarily by differentiated syncytiotrophoblasts and represents a key embryonic signal that is essential for the maintenance of pregnancy 6.
• hCG can activate various signaling cascades and has specialized roles in promoting angiogenesis, maintaining myometrial quiescence, and fostering immunomodulation at the maternal-fetal interface 6.
• hCG has various clinical applications, including diagnosis and monitoring of pregnancy and pregnancy-related disorders, as well as cancer surveillance 6.