Egg freezing – how does it work, and what happens when?

Let’s start with a quick high-level overview of how egg freezing works, what happens during the process leading up to the actual freezing, and what the timeline typically looks like. We also have an abbreviated version here

How does egg freezing work?

Whenever women ovulate, they typically release one mature egg that’s ready to be fertilized. However, at the beginning of each menstrual cycle, there’s more than one immature egg ready to develop: 10-20 ovarian follicles (tiny fluid-filled sacs that each contain an immature egg cell) are typically activated with each cycle; the number and quality have been shown to decline with age. With only one mature egg getting released during typical ovulation, the remainder disintegrate.

Egg freezing and in-vitro fertilization (IVF) take advantage of the eggs that would otherwise disintegrate. Follicle-stimulating hormones are used to get as many follicles as possible to produce mature eggs during the treatment cycle. When the eggs are close to being mature inside the follicles, a shot of another hormone is administered to prevent the follicles from releasing the eggs. A third shot makes sure that the each egg fully matures to contain the appropriate number of chromosomes.

36h after this third shot, the mature eggs are surgically retrieved from each of the follicles, typically under 15min anesthesia. An embryologist then examines the retrieved eggs and flash-freezes those that are fully mature. Later on, the eggs can be thawed if a woman undergoes the remainder of the IVF procedure, which involves fertilizing and implanting one or several of the thawed younger eggs.

Typical steps & timeline:

1. Preparation (at least 2 weeks):

  • Diagnostic tests to better understand the state of your fertility and your likely response to medications to make sure you’re a good candidate for egg freezing; the tests involve a pelvic ultrasound to get a count of the ‘activated’ follicles on your ovaries, typically also a range of blood tests
  • Potential changes to birth control (e.g., you may go on/off birth control to get better reads of certain tests or be able to predict the timing of your next period)
  • Initial virtual or in-person meeting with your doctor at a fertility clinic
  • Personalized plan and timeline for the actual treatment
  • Ordering medications

[This prep phase has the most variable timeline depending on your and your doctor’s schedule, your doctor’s specific requirements for diagnostic tests, the timing of your cycle (some tests can only be done on certain days), and order time for meds]

2. Hormonal injections (1-2 weeks, usually starting at the beginning of your cycle, shortly after you get your period):

  • Daily self-injections of follicle-stimulating hormones that your body naturally produces and that make your follicles grow
  • Regular ultrasound appointments to check on the growth of your follicles and hormone levels to adjust meds if necessary
  • Increased bloating around your ovaries as the follicles grow
  • Anti-ovulation shot when the follicles are large enough to contain mature eggs
  • Trigger shot to get the eggs to fully mature

[Duration of this phase depends on how quickly your follicles mature]

3. Retrieval (15min):

  • Surgical retrieval of the eggs from their follicles 36h after the trigger shot, typically under 15-min anesthesia
  • Recovery of a few hours or days, typically women experience some soreness; bloating is gone as soon as you get your next period and everything ‘resets’

4. Freezing & storage:

  • Examination of the extracted eggs to make sure they’re mature
  • Actual freezing (typically now flash-freezing, also called vitrification) and storage at the clinic



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