Egg freezing (oocyte cryopreservation) is a process that allows individuals to preserve their fertility for future use. This medical procedure requires temporarily overriding the body’s natural reproductive cycle to maximize the number of eggs collected in a single attempt. The process relies on the precise administration of hormonal medications, delivered through subcutaneous injections, to ensure the ovaries produce and mature multiple eggs for retrieval.
The Purpose of Hormonal Injections
The fundamental reason for using injections in egg freezing is to achieve controlled ovarian hyperstimulation. In an unstimulated cycle, the body naturally matures and releases only one egg. The goal of fertility preservation is to retrieve a much larger number of mature eggs to increase the probability of a future successful pregnancy.
Hormonal injections introduce high doses of exogenous gonadotropins, which are protein hormones that directly stimulate the ovaries. This external input bypasses the body’s self-regulating mechanism, allowing multiple follicles (the sacs containing the eggs) to grow simultaneously. The medical team monitors this growth through ultrasound and blood tests to control the timing and extent of the ovarian response before collection.
Daily and Total Injection Count
The duration and number of daily injections are highly individualized, determined by the patient’s age, ovarian reserve, and response to the medication protocol. The main stimulation phase, where most injections are given, typically lasts between 8 and 14 days. During this period, patients generally administer between one and three separate injections each day.
Injections often start with a single daily shot, but a second or third daily injection is introduced as the cycle progresses to prevent premature ovulation. For example, a 12-day protocol requiring two to three injections daily could result in 24 to 36 stimulation shots.
The final, single injection, known as the “trigger shot,” is administered precisely 34 to 36 hours before the scheduled egg retrieval. A complete egg freezing cycle involves a total count that typically falls within the range of 10 to over 40 injections.
Types of Medications Used in the Cycle
The injectable medications used in an egg freezing cycle fall into three primary functional categories, each serving a distinct purpose in the controlled stimulation process.
Gonadotropins
This is the most common medication class, responsible for stimulating the growth of ovarian follicles. These medications contain recombinant or highly purified forms of Follicle-Stimulating Hormone (FSH) and sometimes Luteinizing Hormone (LH). FSH-only products (like follitropin alfa or beta) and combination products (like human menopausal gonadotropin, hMG) are used to promote the maturation of multiple eggs.
Suppressants
Suppressants are introduced to prevent the body from ovulating prematurely. These are Gonadotropin-Releasing Hormone (GnRH) antagonists or agonists, which block the natural hormonal surge that would cause the spontaneous release of eggs before retrieval. GnRH antagonists (such as cetrorelix or ganirelix) are typically added partway through the stimulation phase and often constitute the second daily injection.
The Trigger Shot
The final, single injection is the trigger shot, administered to complete the final maturation of the eggs. This shot uses either human Chorionic Gonadotropin (hCG) or a GnRH agonist (like leuprolide acetate), mimicking the natural LH surge to prepare the eggs for collection.
Managing the Injection Process
All injections required for the egg freezing cycle are designed for self-administration, typically given subcutaneously into the fatty tissue just beneath the skin. The most common injection sites are the lower abdomen or the upper thigh, which are easily accessible and contain minimal nerve endings. The needles used are very fine and short, contributing to the minimal discomfort associated with the daily process.
Proper timing of the injections is important, especially for the trigger shot, which must be administered at a precise hour to ensure the eggs are ready for retrieval. Patients receive comprehensive training from a nurse on the correct technique, including how to mix any powdered medications, draw the correct dosage, and safely inject the medication.
After use, all needles and syringes must be placed into a designated sharps container for safe disposal. Localized side effects, such as mild bruising, redness, or temporary stinging at the injection site, are common and generally manageable throughout the stimulation period.