71 terms explained

Egg Freezing Glossary: A to Z

Clear, plain-English definitions of the medical terms you will hear during fertility assessments, ovarian stimulation, egg collection and storage.

Antral Follicle Count (AFC): The number of small follicles visible in the ovaries during a transvaginal ultrasound. It helps estimate how the ovaries may respond to fertility medication.
Anti-Müllerian Hormone (AMH): A hormone produced by small follicles in the ovaries. An AMH blood test provides an indication of ovarian reserve and can help clinicians plan the dosage of stimulation medication. It does not directly measure egg quality or guarantee the number of eggs that will be collected.

Baseline Scan: An ultrasound performed before ovarian stimulation begins to examine the ovaries, count follicles and check the uterine lining.
Blastocyst: An embryo that has developed for approximately five or six days after fertilisation. This stage becomes relevant when frozen eggs are later thawed and used.

Cancellation: The decision to stop a treatment cycle before egg collection, usually because the ovaries have responded too little or too strongly to medication.
Chromosomes: Structures inside cells that carry genetic information. Chromosomal abnormalities in eggs become more common with age.
Consent Forms: Legal documents specifying how eggs may be stored, used or disposed of. Patients must provide the appropriate consent before their eggs can be frozen and stored.
Cryopreservation: The process of freezing and storing biological material, including eggs, sperm and embryos, at extremely low temperatures.
Cycle: One complete round of treatment, generally including ovarian stimulation, monitoring, the trigger injection and egg collection.

Donor Eggs: Eggs provided by another person for use in fertility treatment.

Egg: The female reproductive cell. The medical term is oocyte.
Egg Collection: The procedure used to remove eggs from the ovarian follicles. It is normally performed using an ultrasound-guided needle while the patient is sedated. It may also be called egg retrieval or oocyte retrieval.
Egg Freezing: A fertility-preservation treatment in which eggs are collected, frozen and stored for possible future use. Freezing eggs does not guarantee a future pregnancy or live birth.
Egg Maturity: The developmental stage of an egg. Usually, only mature eggs can be frozen for future fertilisation.
Egg Quality: An egg's ability to fertilise and develop into a healthy embryo. Egg quality is strongly associated with age and cannot be measured directly through an AMH test.
Egg Retrieval: Another term for egg collection.
Egg Storage: The preservation of frozen eggs at a licensed fertility clinic or storage facility until they are used, transferred elsewhere or disposed of.
Embryo: The early stage of development following the fertilisation of an egg by sperm.
Embryo Freezing: The freezing and storage of fertilised eggs that have developed into embryos. Unlike egg freezing, it requires sperm at the time of treatment.
Embryologist: A specialist who examines, handles, freezes, thaws and fertilises eggs and embryos in a laboratory.
Estradiol or Oestradiol (E2): A form of oestrogen produced by developing follicles. Blood levels may be monitored during ovarian stimulation.

Fertilisation: The process in which sperm enters an egg, creating an embryo.
Follicle: A small, fluid-filled sac inside an ovary that contains an immature egg.
Follicle-Stimulating Hormone (FSH): A hormone involved in follicle growth. Injectable FSH medication is commonly used during ovarian stimulation to encourage several follicles to develop.
Follicular Phase: The first part of the menstrual cycle, beginning on the first day of a period and ending at ovulation.
Fertility Assessment: A combination of consultations, blood tests and ultrasound scans used to evaluate reproductive health and likely response to treatment.
Fertility Preservation: The process of storing eggs, sperm, embryos or reproductive tissue for possible future use.
Frozen Egg Transfer: This is not technically a direct transfer of an egg. Frozen eggs must first be thawed and fertilised, after which a resulting embryo may be transferred into the uterus.

Gonadotrophins: Hormonal fertility medicines, usually containing FSH or a combination of FSH and LH, used to stimulate the ovaries.
GnRH Agonist: A medication that may be used to control ovulation or as a trigger injection in certain treatment protocols.
GnRH Antagonist: A medication used during stimulation to prevent premature ovulation before egg collection.

Hormone Blood Tests: Blood tests used to assess ovarian reserve, monitor follicle development or determine when egg collection should take place.
Human Chorionic Gonadotrophin (hCG): A hormone sometimes used as the final trigger injection to help eggs complete maturation before collection.

ICSI - Intracytoplasmic Sperm Injection: A fertility technique in which one sperm is injected directly into an egg. ICSI is commonly used to fertilise previously frozen eggs after they have been thawed.
Immature Egg: An egg that has not reached the stage required for standard freezing and future fertilisation.
In Vitro Fertilisation (IVF): A treatment in which eggs are fertilised with sperm in a laboratory. Frozen eggs must be thawed and used as part of an IVF or ICSI treatment cycle to attempt pregnancy.
Injection Training: Guidance provided by a clinic explaining how and when to administer fertility medication at home.

Live Birth Rate: The proportion of treatment cycles or embryo transfers that result in the birth of a living baby. Clinics may calculate this rate differently, so the denominator should always be checked.
Luteinising Hormone (LH): A reproductive hormone involved in ovulation and egg maturation.

Mature Egg: An egg that has reached the metaphase II, or MII, stage and is generally suitable for freezing or fertilisation.
Metaphase II (MII) Egg: The stage at which an egg is considered mature. These are normally the eggs selected for vitrification.
Menstrual Cycle: The hormonal cycle that prepares the body for ovulation and a possible pregnancy.
Monitoring Scan: An ultrasound performed during ovarian stimulation to measure the number and size of developing follicles.

Oestradiol: The UK spelling of estradiol, a form of oestrogen that may be measured during treatment.
Oestrogen: A group of hormones produced mainly by the ovaries. Oestrogen levels usually rise as follicles grow.
Oocyte: The medical term for an egg cell.
Oocyte Cryopreservation: The clinical term for egg freezing.
Oocyte Retrieval: The clinical term for egg collection.
Ovarian Hyperstimulation Syndrome (OHSS): A potential complication of fertility medication in which the ovaries respond excessively. Symptoms can range from mild bloating and discomfort to more serious complications requiring medical care.
Ovarian Reserve: An indication of the number of eggs remaining in the ovaries. It may be assessed using AMH, AFC and sometimes FSH. Ovarian-reserve tests help predict response to stimulation but do not provide a precise egg count.
Ovarian Stimulation: The use of hormonal medication to encourage multiple follicles to develop during one treatment cycle.
Ovary: One of the reproductive organs that stores eggs and produces hormones.
Ovulation: The release of an egg from an ovary. During egg-freezing treatment, medication is used to prevent ovulation from occurring before egg collection.

Premature Ovulation: Ovulation that occurs before the scheduled egg collection, meaning some or all of the eggs may no longer be available for retrieval.
Primordial Follicle: An extremely small, early-stage follicle containing an immature egg. These follicles are not directly counted during a standard ultrasound.
Protocol: The personalised treatment plan specifying which medicines to take, their dosage and when they should be administered.

Retrieval Rate: The relationship between the number of follicles seen and the number of eggs successfully collected. Not every follicle necessarily contains a retrievable egg.

Sedation: Medication used during egg collection to make the patient sleepy, comfortable and less aware of the procedure.
Slow Freezing: An older cryopreservation method in which eggs are cooled gradually. Most modern egg-freezing treatment uses vitrification instead.
Social Egg Freezing: Egg freezing undertaken for personal or non-medical reasons. It may also be described as elective egg freezing or planned egg freezing.
Stimulation Medication: Hormonal injections used to encourage several follicles to grow simultaneously.
Storage Period: The length of time for which frozen eggs are legally authorised and consented to remain in storage.

Thawing: The controlled warming of frozen eggs before they are assessed and potentially fertilised.
Thaw Survival Rate: The percentage of frozen eggs that remain viable after warming. Survival does not mean that an egg will necessarily fertilise or produce a viable embryo.
Transvaginal Ultrasound: An internal ultrasound used to examine the ovaries, count follicles and monitor follicle growth.
Trigger Injection: The final injection administered before egg collection. It helps the eggs complete their maturation and must usually be taken at a precise time.

Ultrasound Monitoring: A series of scans used to track follicle development and determine the appropriate time for the trigger injection and egg collection.
Uterus: The organ in which an embryo may implant and a pregnancy develops. It is also commonly called the womb.

Vitrification: A rapid-freezing technique used to cryopreserve eggs. It reduces the formation of damaging ice crystals and is now widely used instead of slow freezing.

Warming: The laboratory term often used instead of thawing for the controlled process of bringing vitrified eggs back to the appropriate temperature.
Womb: The everyday term for the uterus.

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This glossary is for general information only and is not medical advice. Always speak to a licensed fertility clinician about your own treatment.