Egg freezing as a practice has been around for decades now, but it is only recently that society has started discussing it in a more open, non-judgmental way. While this is a positive leap in how society views individuals’ fertility choices, the accuracy and robustness of the scientific process is still gaining ground with the public. As a measure to help you understand the terminology surrounding egg freezing better, we have come up with a list of words that are associated with egg freezing and often appear in infographics, brochures, leaflets, and other resources but have the potential to leave one feeling confused. 

 

We hope this egg freezing dictionary will help you better understand information the next time you read a brochure or come across an advert.

First Things First – The Considerations

1. Medical egg freezing – This type of  egg freezing is done for medical reasons (e.g., before chemotherapy).
2. Elective or social egg Freezing – Egg freezing which is done for non-medical reasons (e.g., delaying childbearing).
   
3. Fertility Preservation – This is a broad term encompassing egg, embryo, and sperm freezing, done for preserving one’s fertility.
4. ART – This stands for assisted reproductive technologies, which encompasses procedures that help individuals conceive when they are facing infertility or other barriers to reproducing. IVF is a type of ART.
   
5. Reproductive Longevity – This refers to reproductive healthspan and extending the reproductive lifespan through processes like preserving fertility potential via egg freezing.
   
6. Storage Fees – Annual fees for keeping eggs frozen in long-term storage. It also applies to the fees for storing embryos and sperm when these are stored long-term. The fees differ across providers. 

Physiology & Organs – The Scientific and Medical terms

1. Ovaries (singular: ovary) – These are a pair of oval-shaped glands on either side of the womb (or uterus). They are the site of production and development of eggs and they also produce female hormones like estrogen and progesterone. 
2. Oocyte and ovum – Both of these are scientific terms which are related to each other and refer to different stages of the egg during its development. Oocyte refers to an egg at an earlier stage in its development journey while ovum (plural: ova) refers to a fully mature egg, once it has completed its development after being fertilized by sperm. In the context of egg freezing we are interested in retrieving the eggs when they are at the oocyte stage from the body. 
3. Follicle – In the simplest terms, a follicle is a fluid filled sac that houses an immature egg and provides nourishment and regulation for the immature egg to develop (1). If the ovary is the house, then each follicle can be analogous to a room in which an egg resides, and there are several of these follicles. The number of remaining follicles in an individual is directly proportional to their fecundity (or potential to reproduce).
4. Gonadotropins (also gonadotrophins) – These are hormones produced by the pituitary gland (a tiny pea-sized organ at the base of the brain), which stimulate the testes and ovaries to produce sperm and eggs, respectively. Follicle stimulating hormone and Luteinising hormone are gonadotropins, which we have discussed below. 
5. Follicle Stimulating Hormone or FSH – This is a gonadotropin which is essential for follicular development in the ovary, i.e. egg development (2). It is administered to stimulate follicles in ART cycles.
6. Anti-Müllerian hormone or AMH – This is a hormone secreted by the ovarian follicles and the levels of AMH directly correlate with the number of early stage follicles in the ovary (3), as such it serves as a surrogate marker for reproductive potential of an individual.
7. Antral follicle count or AFC – This is the number of developing follicles visible (visualised through an ultrasound) in your ovaries during the early phase of your cycle. A higher AFC generally suggests a greater egg reserve.
8. Luteinising hormone or LH – This is another hormone that supplements FSH to help in egg development and it surges just before ovulation in the natural cycles (4). It is sometimes used in ART cycles to support egg development and retrieval (5).
9. Ovarian reserve tests – These are tests which have been devised to predict how many viable eggs would an individual stimulated by the right hormones be able to produce. This is done by measuring the levels of FSH and AMH (which we have defined above) usually accompanied by conducting an ultrasound to count the number of growing follicles within the ovaries (AFC). In simple terms ovarian reserve refers to the number of eggs an individual would have.

Logistics & Outcomes – The Process

1. Cycle – In physiological terms, this refers to the rhythmic production, release, and elimination of an egg in the female reproductive tract every month, commonly referred to as the menstrual cycle or periods. However, in the context of egg freezing the ‘cycle’ is a bit modified as hormones are injected into the body to stimulate the ovaries to produce multiple eggs instead of one, and then artificially retrieving these eggs (6). As such in the egg freezing context, one cycle refers to a course of 10-12 days when patients self-administer hormones to stimulate egg production and then finally these eggs are retrieved through a minimally invasive surgical procedure. 
2. Mature eggs – The development of eggs in the ovary in one cycle, and throughout an individual’s life, is a complex process. During birth, the ovaries already have all the precursors (follicles, which we discussed earlier) to the eggs they will ever produce in the individual’s lifetime but these precursors are at an early stage of egg development. After puberty, each menstrual cycle pushes a set of these follicles to develop. And one or in some cases two of these follicles will mature and be released (in a process called ovulation) (1). It is this stage of the egg that can be fertilised, so ART cycles require eggs to be at this ‘mature’ stage for conception purposes.
3. Trigger shot – This refers to the administration of a shot of hormone(s) to “trigger” the maturation of eggs (6). The most common hormone used is human chorionic gonadotropin (hCG), as its structure mimics that of LH (previously described) and can bind to the same receptors to stimulate egg maturation (7). The other candidate for a trigger shot is GnRH agonists (GnRH – Gonadotropin-Releasing Hormone ; agonist – a molecule that mimics other hormones and stimulates the production of GnRH). hCG and GnRH agonists are sometimes also used in conjunction for a stronger effect (8). A trigger shot is administered approximately 36 hours before egg retrieval to mimic the natural hormones released in the body immediately preceding ovulation. This process is time sensitive and as such administration of the trigger shot is dependent on the time of egg retrieval.
4. Vitrification – It is a common procedure used in egg freezing and involves the rapid cooling of samples, in this case eggs, without forming damaging ice crystals, thus maintaining the integrity of the eggs. While the technique is gaining popularity now, Rall & Fahy (1985) reported the first mouse to be obtained after embryo vitrification, so the process has been around since then (9).
5. Thawing – It is the process by which frozen eggs are warmed up and brought to a stage where they can be used for fertilisation. 
6. Success rate – This figure usually refers to the number of live births per egg frozen. It is important to note that the success rate is dependent on various factors, one of the most important being the quality of the eggs frozen which is directly dependent on the age of the person when their eggs were frozen. 

We hope that you are now more familiar and comfortable with the jargon surrounding egg freezing. Egg freezing is only the beginning of the process, as the journey to a pregnancy also involves retrieval of these frozen eggs and going through IVF to create embryos which are then transferred to the womb. 

At OvoLife we aim to raise awareness about fertility preservation and create a library of information that provides freely accessible information for all. This glossary of common terms, is an attempt of ours to make egg freezing and the terminology surrounding the process more interpretable and understandable for everyone so that preserving fertility becomes an informed decision for all.

 

This article was written by: Ninisha Barman, BSc (Imperial College London), MPhil (University of Cambridge), Research Assistant (University of Oxford)

 

Resources:

1. Gosden, R. and Lee, B., 2010. Portrait of an oocyte: our obscure origin. The Journal of clinical investigation, 120(4), pp.973-983. https://doi.org/10.1172/JCI41294
2. Raju, G.A.R., Chavan, R., Deenadayal, M., Gunasheela, D., Gutgutia, R., Haripriya, G., Govindarajan, M., Patel, N.H. and Patki, A.S., 2013. Luteinizing hormone and follicle stimulating hormone synergy: A review of role in controlled ovarian hyper-stimulation. Journal of human reproductive sciences, 6(4), pp.227-234. https://doi.org/10.4103/0974-1208.126285
3. Hansen, K.R., Hodnett, G.M., Knowlton, N. and Craig, L.B., 2011. Correlation of ovarian reserve tests with histologically determined primordial follicle number. Fertility and sterility, 95(1), pp.170-175. https://doi.org/10.1016/j.fertnstert.2010.04.006
4. Kumar, P. and Sait, S.F., 2011. Luteinizing hormone and its dilemma in ovulation induction. Journal of human reproductive sciences, 4(1), pp.2-7. 10.4103/0974-1208.82351
5. Pezzuto, A., Ferrari, B., Coppola, F. and Nardelli, G.B., 2010. LH supplementation in down-regulated women undergoing assisted reproduction with baseline low serum LH levels. Gynecological Endocrinology, 26(2), pp.118-124. https://doi.org/10.3109/09513590903215516
6. Maghraby, H., Saleh, H., Fourtia, I.L., Rasheed, S., Elmahdy, M., Abdelbadie, A.S., Di Guardo, F., Drakopoulos, P., Midassi, H. and Shoukry, A., 2024. The dilemma of the trigger timing in IVF: a review. Middle East Fertility Society Journal, 29(1), p.8. https://doi.org/10.1186/s43043-024-00166-w
7. Tobler, K.J., Zhao, Y., Weissman, A., Majumdar, A., Leong, M. and Shoham, Z., 2014. Worldwide survey of IVF practices: trigger, retrieval and embryo transfer techniques. Archives of gynecology and obstetrics, 290(3), pp.561-568. https://doi.org/10.1007/s00404-014-3232-6
8. Haas, J., Bassil, R., Samara, N., Zilberberg, E., Mehta, C., Orvieto, R. and Casper, R.F., 2020. GnRH agonist and hCG (dual trigger) versus hCG trigger for final follicular maturation: a double-blinded, randomized controlled study. Human Reproduction, 35(7), pp.1648-1654. https://doi.org/10.1093/humrep/deaa107
9. Rall, W.F. and Fahy, G.M., 1985. Ice-free cryopreservation of mouse embryos at− 196 C by vitrification. Nature, 313(6003), pp.573-575. https://doi.org/10.1038/313573a0