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Abnormal fertilisation
A proportion of the inseminated oocytes after IVF or ICSI either form only 1 pronucleus or multiple pronuclei (3 or more). These are considered abnormally fertilised oocytes and can not be used for treatment
The legal process in which people adopt a child and become their legal parents.
The medical practice dealing with the health of the male reproductive system.
Absence of ovulation
Anti–Müllerian Hormone (AMH)
A hormone produced by the granulosa cells, which envelop each oocyte and provide them energy. AMH can also serve as a molecular biomarker for relative size of the ovarian reserve. In humans, this is helpful because the number of cells in the follicular reserve can be used to predict timing of menopause and the response to ovarian stimulation.
Antral follicles
Resting follicles that appear as a small fluid-filled sacs which contain an immature egg. These follicles can be measured and counted on cycle days 2, 3 and 5 and this can be used to assess the ovarian reserve.
Assisted reproductive technology (ART)
Laboratory processes that involve the in vitro handling of both human oocytes and sperm or of embryos for the purpose of reproduction. This includes, IVF and embryo transfer, intracytoplasmic sperm injection (ICSI), embryo biopsy, preimplantation genetic testing PGT, gamete and embryo cryopreservation, semen, oocyte and embryo donation, surrogacy, intra uterine insemination with either male partner or donor sperm.
The complete absence of sperm in the ejaculate. This is diagnosed by doing a sperm analysis and it needs confirmation with a second sperm analysis.
Biochemical pregnancy
The absence of an identifiable pregnancy on ultrasound scan despite a positive pregnancy test. Its name comes from the fact that the pregnancy is detected by biochemical tests like urine pregnancy tests or blood tests but then ends at a very early stage.
The stage of embryo development that occurs around day 5–6 after insemination or ICSI. The blastocyst contains a fluid filled central cavity (blastocoele), an outer layer of cells (trophectoderm) and an inner group of cells (inner cell mass).
Body Mass Index (BMI)
Measure of body mass determined by dividing a person’s weight (in kilograms) by height (in metres) squared. Normal values are between 20 and 25.
Cancelled IVF/ICSI cycle
A cycle in which ovarian stimulation has been started but which did not proceed to oocyte collection. This could be due to a lack of response to stimulation or to other medical or personal reasons
Cancelled frozen embryo transfer
A cycle in which a thawed or warmed embryo did not proceed to embryo transfer. This could be due to the response to the medication, personal or medical reasons, or to lack of survival of the embryo/s
This is a fine tube put into the body. In fertility it nearly always refers to a catheter put into the uterus for embryo transfer in IVF or insemination in IUI.
The lower part of the uterus in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape. It is through this canal that the embryos are transferred to the uterus in an IVF or ICSI cycle and the sperm is placed in the uterus in an IUI cycle.
Cervical mucus
A fluid produced by the cervix that enhances the transport of the sperm into the endometrial cavity. Just before ovulation occurs, the hormone oestrogen leads to increased cervical mucus and changes it into a stretchy, viscous-like substance. This helps sperm survive and swim.
Cleavage stage embryos
Embryos beginning with the 2-cell stage during the second and third day of normal embryo development. At this stage the cells of the embryo can be counted under the microscope.
Sexually transmitted infection that may damage the reproductive system
Clinical pregnancy
Confirmation of a pregnancy with ultrasound by visualising one or more gestational sacs.
Clinical pregnancy rate
The number of clinical pregnancies expressed per 100 started cycles, egg collection cycles or embryo transfer cycles.
Clomiphene Citrate
A fertility drug used to induce the growth of one or more follicles and ovulation
Before fertility treatment can take place, patients are required by law to give their informed consent to ensure their sperm, eggs, embryos and personal information are used in a way that they are happy with
Corpus luteum
A follicle that has released the oocyte. The corpus luteum produces oestrogen and progesterone. If pregnancy does not occur, the corpus luteum stops producing Progesterone and the female will have a menstrual bleed
The process of slow freezing or vitrification to preserve oocytes, sperm and embryos at –196°C in liquid nitrogen. They can be stored for many years without decrease in viability.
Undescended testes. It can lead to male infertility
Day 1
The first day of the period, meaning the first day of full flow (spotting doesn’t count)
Donor Insemination
The process of placing donated sperm that has been prepared in the laboratory into the uterus around the time of ovulation with the aim of achieving a pregnancy
Pain with the menstrual bleeding
Ectopic Pregnancy
A pregnancy outside the uterine cavity, usually in the fallopian tube. It is diagnosed by ultrasound, surgical visualization, clinical symptoms, or histopathology.
Elective Single Embryo Transfer (eSET)
The transfer of the embryo of highest quality selected from a group of embryos. This is done to maximize the chances of a singleton pregnancy in patients younger than 37 who have good quality embryos.
Early stages of development of the fertilized oocyte, until eight weeks after fertilization.
Embryo Fragmentation
The proportion of membrane vesicles that are shed by the cells as the embryo divides. This gives an indication of embryo quality.
Embryo Transfer (ET)
Placement into the uterus of one or two embryos at any embryonic stage from day 2 to day 6 after IVF or ICSI or after thawing or warming. This is done with a full bladder and under ultrasound guidance.
A condition where tissue similar to the lining of the womb starts to grow in other places, such as the ovaries and fallopian tubes. Endometriosis can affect women of any age. It’s a long-term condition that can have a significant impact on your life as it causes several degrees of pain. It can be a cause of infertility in women.
The lining of the uterus that grows throughout the menstrual cycle and is shed in the monthly menstrual cycle if an embryo does not implant.
A convoluted, highly coiled duct that stores and transports the sperm from the testicle to the vas deferens at the point of ejaculation.
Hormone secreted by the ovaries as the follicles grow.
Fallopian Tubes
Tubes connected to the uterus and positioned near the ovaries. It is here that fertilization happens and embryo development starts.
Female Infertility
Infertility caused primarily by female factors including: ovulatory disorders; diminished ovarian reserve; tubal obstruction; endocrine, genetic, functional or immunological abnormalities of the reproductive system; chronic illness; and sexual conditions incompatible with sexual intercourse.
The process that involves a sperm entering a mature oocyte after which two pronuclei appear, one from the oocyte and one from the sperm. The appearance of these two pronuclei allows embryologists to decide which oocytes are fertilized and which aren’t the day after oocyte collection.
Fertility Care
Interventions that include fertility awareness, support and fertility management with an intention to assist people to achieve their wish to build a family.
Fertility Consent
A ready to use library of materials which explains each fertility treatment and each HFEA form. It allows patients to log in through a portal and access treatment information as well as consent forms which can be completed online, at home or in the clinic.
Fertility Counselling
It provides an opportunity to explore any emotional difficulty, fears and anxieties, or distress that people might experience during their fertility journey with a professional counsellor. It can help to cope, make choices, and receive independent support. It is a mandatory part of treatment if you are giving or receiving donated gametes or embryos.
Fertility Preservation
Treatments including cryopreservation of oocytes, sperm and embryos to preserve reproductive capacity. These procedures can be offered to patients about to undergo treatments that will render them infertile, like cancer therapies or gender reassignment and to patients who wish to postpone the time to become parents.
Benign (usually non-cancerous), muscular growth commonly found in the uterus.
Follicle Stimulating Hormone (FSH)
A hormone produced by the pituitary gland that stimulates the growth of the follicles that contain the oocytes in the ovary. It is given to patients to stimulate the growth of multiple follicles in IVF and ICSI cycles. In males it contributes to the production of sperm.
A fluid filled sac in the ovary in which an oocyte grows and develops. Although the oocyte is microscopic the follicles can be visualized by ultrasound.
Freeze-All Cycle
An IVF or ICSI cycle in which, after oocyte aspiration, all suitable embryos are cryopreserved and no embryos are transferred to a woman in that cycle. This is usually done for fertility preservation or to minimize the risk of ovarian hyperstimulation syndrome. The cryopreserved embryos have a very similar chance of success to the fresh embryos and those remain the same no matter how long they are kept in storage.
Frozen-Thawed Embryo Transfer (FET) Cycle
A fertility treatment in which cycle monitoring is carried out with the intention of transferring to a patient, frozen/thawed or vitrified/warmed embryo/s. A FET cycle can take place during a natural menstrual cycle or by using medication. The monitoring of the cycle is done by ultrasound scanning.
Frozen-Thawed Oocyte Cycle
A fertility treatment in which cycle monitoring is carried out with the intention of fertilizing thawed/warmed oocytes and performing an embryo transfer. The preparation and monitoring are the same as an FET cycle.
Full Bladder
A full bladder is required for embryo transfers as it creates a reservoir of fluid that enhances the movement of sound waves through the abdominal cavity. This creates a clearer view of the structures that need to be observed. It also flattens the uterus which facilitates its access with the embryo transfer catheter.
Female oocytes and male sperm
Gestational Age
In pregnancies that result from fertility treatment it is calculated by adding two weeks (14 days) to the number of completed weeks since fertilization occurred in the laboratory
Gestational Sac
A fluid-filled structure associated with early pregnancy, which may be located inside or, in the case of an ectopic pregnancy, outside the uterus.
Gonadotropin Releasing Hormone (GnRH)
A hormone produced by the Hypothalamus that stimulates the production of LH and FSH.
GnRH Agonist
A type of medication which affects LH and FSH as well as sex hormones. They are used for a variety of indications including in fertility medicine and to lower sex hormone levels and allow for ovarian stimulation.
GnRH Antagonist
Medication used in IVF and ICSI cycles to prevent a premature LH rise which could lead to premature luteinization, follicle maturation arrest and asynchrony of oocyte maturation. It is an injection given midway through the FSH injections of an IVF or ICSI cycle to block release of the eggs.
The hormones produced by the pituitary gland that control reproductive function and are part of the reproductive cycle, i.e. FSH and LH.
Granulosa Cells
Cells that surround each oocyte and line each follicle and are responsible for feeding the egg with nutrients and producing estrogen.
The process by which an embryo at the blastocyst stage extrudes out of, and ultimately separates from, the zona pellucida just before implantation.
Hepatitis B
Patients undergoing fertility treatment need to be tested for Hepatitis B to prevent it from being passed onto the mother (in the case of infected male) or child.
Hepatitis C
Patients undergoing fertility treatment need to be tested for Hepatitis C to prevent it from being passed onto the mother (in the case of infected male) or child.
Patients undergoing fertility treatment need to be tested for HIV to prevent it from being passed onto the mother (in the case of infected male) or child.
Human Chorionic Gonadotropin (hCG)
A hormone that is produced by the developing placenta in the early stages of pregnancy. It enables the corpus luteum to continue producing Progesterone. In assisted conception hCG is sometimes used 36 hours prior to oocyte retrieval to mature the eggs ready for the oocyte collection procedure.
Human Fertilisation and Embryology Authority (HFEA)
Government regulator responsible for making sure fertility clinics and research centres comply with the law. They provide free, clear and impartial information on UK fertility clinics, IVF and other types of fertility treatment, and donation.
Fluid in the fallopian tube.
Hystero Contrast Sonography (Hycosy)
A procedure that uses ultrasound to check the patency of the fallopian tubes.
Hystero-Salpingogram (HSG)
A procedure which uses X-ray to check the patency of the fallopian tubes and the uterus.
A procedure in which the uterine cavity is visualized by a surgeon. It can help in the diagnosis of fibroids or polyps.
IDEAS Patient Portal
A portal that enables secure messaging between the service and the patients with calendars, forms, results, and document download through the fertility software IDEAS.
Immature Oocyte
An oocyte that has not yet reached maturity and the ability to be fertilized. It can be either at the Metaphase I (MI) or at the germinal vesicle (GV) stage.
The attachment and subsequent penetration by a hatched blastocyst into the endometrium. This process starts 5 to 7 days after fertilization of the oocyte usually resulting in the formation of a gestational sac.
The same as subfertility.
Inner Cell Mass
A group of cells attached to the trophectoderm consisting of embryonic stem cells, which have the potential to develop into cells and tissues in the human body and will become the fetus if the embryo implants.
Placing sperm into the uterus, or in IVF placing sperm with the eggs in a culture dish in the laboratory.
Intracytoplasmic Sperm Injection (ICSI)
A procedure in which a single sperm is injected into the oocyte cytoplasm. It is used when sperm concentration, motility, and/or morphology are low or when there has been failed fertilization with IVF before.
Intra-Uterine Insemination (IUI)
A procedure in which laboratory processed sperm are placed in the uterus using a fine catheter to attempt a pregnancy.
In Vitro Fertilization (IVF)
The incubation of oocytes with sperm prepared in the laboratory in vitro for the purpose of fertilization. On average 70% of the inseminated oocytes will fertilize in vitro.
Klinefelter’s Syndrome
A genetic condition whereby males have an extra X chromosome and it can cause infertility.
Technique in which a telescope visualizes the structures within the abdomen. Commonly used to check tubal patency and the presence of any pelvic pathology.
Last Menstrual Period
Luteinising Hormone (LH)
One of the hormones produced by the pituitary gland in the brain. A rapid rise of LH initiates the onset of ovulation.
Male Infertility
Infertility caused primarily by male factors encompassing: abnormal semen parameters or function; anatomical, endocrine, genetic, functional or immunological abnormalities of the reproductive system; chronic illness; and sexual conditions incompatible with the ability to have sexual intercourse.
Mature Oocyte
An oocyte at metaphase of meiosis II, exhibiting the first polar body and with the ability to become fertilized.
Menstrual Cycle
A cycle of normally 28 days in which ovulation occurs around day 14 and if fertilization does not occur, results in a bleed around day 28.
The spontaneous loss of pregnancy before 24 weeks of gestation.
An embryo formed after completion of compaction, typically 4 days after IVF or ICSI.
Multiple Birth
The birth of more than one fetus.
Multiple Pregnancy
A pregnancy with more than one embryo or fetus.
Non-Obstructive Azoospermia
Absence of sperm in the ejaculate due to lack of production of mature sperm.
Obstructive Azoospermia
Absence of sperm in the ejaculate due to occlusion of the ductal system. Trauma or infection can cause this condition.
Ongoing Clinical Pregnancy
A clinical pregnancy of one or more gestational sacs with a discernible heartbeat.
The female gamete (egg).
Oocyte Collection
Ovarian follicular aspiration performed with the aim of retrieving oocytes from the follicles growing in the ovaries for IVF or ICSI treatment.
Oocyte Donation
The use of oocytes collected from an oocyte donor for the creation of embryos and embryo transfer into an oocyte recipient.
Oocyte Cryopreservation
The freezing or vitrification of oocytes for future use.
Oocyte Maturation Triggering
An injection given to induce the oocytes developing in the ovaries as a result of ovarian stimulation to reach maturity. On average, 80% of the oocytes collected are mature.
Oocyte Recipient Cycle
A cycle in which a patient receives oocytes from a donor, or her partner if in a same-sex relationship, to be used for fertility treatment.
Ovarian Cyst
A sac filled with fluid or semisolid material that develops on or within the ovary. Most cysts are benign and disappear spontaneously without the need for treatment.
Ovarian Hyperstimulation Syndrome (OHSS)
An over response to ovarian stimulation, in which the ovaries enlarge and there may be nausea, abdominal swelling, and shortness of breath. If these symptoms develop, the patient is asked to contact the clinic immediately. OHSS may be classified as mild, moderate, or severe according to the degree of abdominal distention, ovarian enlargement, and respiratory, haemodynamic, and metabolic complications.
Ovarian Reserve
A measure of the number and/or quality of oocytes in the ovaries, reflecting the ability to reproduce. Ovarian reserve can be assessed by any of several means. They include: female age; number of antral follicles on ultrasound; anti-Mullerian hormone levels; follicle-stimulating hormone; response to gonadotropin stimulation, and oocyte and/or embryo assessment during fertility treatment, based on the number and morphology of the oocytes and/or embryos.
Ovarian Stimulation
Initial part of the IVF/ICSI cycle where the patient is given injections of different drugs to induce the development of multiple ovarian follicles. Intrauterine insemination cycles can also sometimes include ovarian stimulation.
The female reproductive organ that produces oocytes on a monthly basis under hormonal influence from the pituitary gland.
The natural process of expulsion of a mature egg from its ovarian follicle. In a menstrual cycle, this happens once a month, usually 14 days before the next menstrual period.
Ovulation Induction (OI)
Treatment of women with absent or irregular cycles with the intention of inducing ovulation. The medications can be in the form of FSH injections or in the form of tablets like Clomiphene Citrate.
Percutaneous Epididymal Sperm Aspiration (PESA)
A surgical procedure in which a needle is introduced into the epididymis with the intention of obtaining sperm by aspiration. This procedure is carried out under local anaesthetics.
Polycystic Ovary Syndrome (PCOS)
A heterogeneous condition, which requires the presence of two of the following three criteria: (1) Infrequent ovulation or anovulation; (2) Hyperandrogenism (3) Polycystic ovaries, as assessed by ultrasound scan with more than 24 total antral follicles (2–9 mm in size) in both ovaries.
The process by which an oocyte is penetrated by more than one sperm.
Preimplantation Genetic Testing (PGT)
A test performed to analyze the DNA from blastocysts to identify embryos carrying specific genetic abnormalities. It includes PGT for monogenic/single gene defects (PGT-M); and PGT for chromosomal structural rearrangements (PGT-SR).
Premature Ovarian Failure
A condition in women younger than age 40 years where the ovaries are no longer producing follicles. This can be due to congenital, genetic, chromosomal, or damage caused by toxic drugs, such as chemotherapy.
Primary Female Infertility
A person who has never been diagnosed with a clinical pregnancy and meets the criteria of being classified as having infertility.
Primary Male Infertility
A person who has never initiated a clinical pregnancy with their sperm and meets the criteria of being classified as infertile.
A female hormone secreted by the corpus luteum in the ovaries during the second half of the menstrual cycle. It thickens the lining of the uterus to prepare for the implantation of a fertilized oocyte.
A round structure in the oocyte surrounded by a membrane. Normally, two pronuclei are seen after fertilization, each containing a haploid set of chromosomes, one set from the oocyte and one from the sperm. Observing 2 pronuclei inside the oocyte allows the embryologists to confirm fertilization.
A person or couple who receives donated eggs, sperm or embryos for the purpose of getting pregnant and with the intention of becoming the legal parent of the child.
Reduced Ovarian Reserve
A reduced number and/or reduced quality of oocytes, such that the ability to get pregnant and have a baby is decreased.
Reproductive Surgery
Surgical procedures performed to diagnose, conserve, correct and/or improve reproductive function in either men or women. Surgery for contraceptive purposes, such as tubal ligation and vasectomy, are also included within this term.
Retrograde Ejaculation
A condition that causes the semen to be forced backward from the ejaculatory ducts into the bladder during ejaculation. In most cases, sperm can be retrieved from the urine and used for fertility treatment, usually ICSI.
RI Witness
Electronic witnessing system that uses Radio Frequency Identification (RFID) to detect and monitor all activity in the IVF Laboratory. The system helps mitigate the risk of human error every time samples are moved from one dish or tube to another and safeguards sperm, oocytes and embryos every step of the IVF/ICSI or IUI cycle.
Secondary Female Infertility
A person unable to get pregnant but who has previously been able to carry a clinical pregnancy.
Secondary Male Infertility
A person who is unable to initiate a clinical pregnancy with their sperm, but who had previously initiated a clinical pregnancy.
Fluid that constitutes the ejaculate.
Semen Analysis
A description of the ejaculate to assess function of the male reproductive tract. Characteristic parameters include volume, concentration, motility, morphology of spermatozoa and presence of other cells.
Semen Volume
The amount of fluid in an ejaculate.
The fluid at ejaculation that contains the sperm, other cells and secretions originating from the testes and sex accessory glands.
Singleton Pregnancy
A single gestation sac/fetus that develops in the womb (the much more common case, in humans). A pregnancy in which one embryo develops in the uterus.
Slow Freezing
A cryopreservation process in which the temperature of the cells is lowered in a step-wise fashion, from room temperature to extreme low temperature (−195.79 °C). This is how sperm is frozen and in the past it was the same procedure for embryos but nowadays they are mostly vitrified (see vitrification).
The male reproductive cell that unites with the oocyte to produce an embryo.
Sperm Concentration
The number of spermatozoa in millions per 1 ml of semen. 15 millions per ml and above is considered normal.
Sperm Preparation
A procedure that involves the separation of sperm through centrifugation and resuspension in culture media. This term is sometimes referred to as ‘sperm washing’. The prepared sperm can be used for IVF, ICSI or IUI.
Sperm Morphology
Percentage of sperm that show a normal shape in semen.
Sperm Motility
The percentage of moving spermatozoa relative to the total number of spermatozoa. 40% motility and above is considered normal.
Sexually transmitted disease infection, such as Chlamydia.
Surgical Sperm Retrieval
Any surgical procedure aimed at retrieving sperm from either the testis or the epididymis. This is performed in men who are azoospermic or unable to produce sperm from ejaculation for any other reason.
The male organ where sperm are produced.
The process of raising the temperature of slow-frozen cells from the storage temperature to room temperature.
Time-lapse Imaging Incubator (Embryoscope)
The photographic recording of microscope image sequences at regular intervals in ART, referring to gametes, zygotes, cleavage-stage embryos or blastocysts.
Cells forming the outer layer of a blastocyst that have the potential to develop into the placenta and amniotic membranes.
Tubal Patency
Openness and lack of blockage of the fallopian tubes.
Tubal Pathology
Tubal abnormality resulting in dysfunction of the Fallopian tube, including partial or total obstruction of one or both tubes, hydrosalpinx (fluid-filled), and/or adhesions (scarring) affecting the normal ovum pick-up function. It usually occurs after pelvic inflammatory disease or pelvic surgery.
Twin Pregnancy
A pregnancy in which two embryos develop in the uterus at the same time.
Ultrasound Scan
A procedure that uses high-frequency sound waves to create an image of part of the inside of the body. During fertility treatment, ultrasound is used to monitor follicle development in the ovaries and the thickness of the endometrial lining. Ultrasound is also used during IVF for oocyte collection, to guide the needle through the vaginal wall to the ovaries. It is also used during embryo transfer to ensure the catheter is in the correct position. It is also used to visualize a pregnancy.
Unexplained Infertility
Infertility in couples with apparently normal ovarian function, Fallopian tubes, uterus, cervix and pelvis and with adequate coital frequency; and apparently normal testicular function, genito-urinary anatomy and a normal ejaculate. The potential for this diagnosis is dependent upon the methodologies used and/or those methodologies available.
An ultra-rapid cryopreservation procedure that prevents ice formation within a cell whose aqueous phase is converted to a glass-like solid.
The canal in the female that leads to the cervix, which leads to the uterus.
The process of raising the temperature of a vitrified cell or cells from the storage temperature to room/physiological temperature.
Y-Chromosome Microdeletions
Missing segments of the genetic material on the Y-chromosome that are associated with abnormal spermatogenesis.
Zona Pellucida
The glycoprotein coat or ‘shell’ surrounding the oocyte.
A single cell resulting from fertilization of a mature oocyte by a sperm and before completion of the first mitotic division.

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