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IVF Glossary

Andrologist – The laboratory personnel who perform the procedures involving semen and sperm.

Andrology Laboratory: The laboratory where sperm is examined and processed for male partners of couples seeking treatment for infertility.

Anti-sperm Antibodies: The products that are formed by the body which recognize sperm as a foreign protein.  These products are located in the body fluids of a man and can cause sperm to clump and to become ineffective in swimming to the egg or penetrating it.  When present in high concentrations, the antibodies can be a factor in reducing a patient’s chances for fertility.  Anti-sperm antibodies can also be present in the body fluids of a woman.

Assisted Hatching: The formation of a small hole in the shell, or zona pellucida, of an embryo by an embryologist for the purpose of facilitating the embryo’s hatching from its shell in the uterus shortly before implantation.

Atretic – Degenerate. Usually in IVF, in reference to an oocyte being defective and incapable of fertilization and growth.

Blastocyst – An embryo stage that develops after the morula stage. The blastocyst is made up of two components, the inner cell mass (ICM) and the trophectoderm.  The trophectoderm surrounds the ICM and a fluid-filled cavity known as the blastocoels.  Blastocyst formation generally takes place on the fifth day of embryo development.

Blastocoel – The fluid-filled cavity of a blastocyst.

Blastomere – A single cell of a multi-cell embryo.

Cell Fragments: Fragments are small portions of a cell that break off the main part of the cytoplasm, or cell material, during the process of cell division.  Since fragments break off the cell, they may carry important parts of the cell with them, including organelles.  If fragments are very plentiful, they may compromise the cell’s ability to metabolize the nutrients in its environment.

Chromosome – A single strand of highly coiled DNA containing many genes. In humans, there are 46 chromosomes, 23 inherited from each parent.

Cleavage – The division of an early embryo. During this stage of development, the number of cells in the embryo increases, but the overall size of the embryo does not change.

Compaction:  The process that an embryo goes through whereby its cells adhere to each other and become less distinct as individual cells.  This is an important growth function and a sign of health that should begin on day 3 and continue until day 4 when the embryo is classified as a morula.
Cortical Granule Reaction – A chemical process that occurs within an oocyte after the penetration by a sperm. This process prevents more than one sperm from entering an oocyte.

Cryopreservation:  The freezing of tissue for the purpose of utilizing it at a later time.  In IVF, this can be eggs, sperm or embryos.  It always involves the initial placement of the tissue in some concentration of a cryoprotectant solution (an alcohol-based product and sucrose) in order to remove water from the cells.  The cells are then cooled in a timed formula that allows the cells to survive the freeze-thaw process.    

Cytoplasm – The part of a cell that is enclosed within the cell membrane (excluding the nucleus). This is where most cellular activity occurs.

Embryo – An oocyte that has been fertilized by a sperm and has undergone cellular division . The term embryo is used from the time of the first cleavage until about eight weeks after fertilization.

Embryo Biopsy – The removal of one or several cells from a preimplantation embryo for the purposes of genetic testing.

Embryologist – The IVF laboratory personnel who perform the procedures involving oocytes and embryos. At Ovation Fertility Austin the embryologists also act as andrologists.

Embryology Laboratory:  The laboratory where eggs and sperm from infertile couples are combined and where their embryos are grown before they are transferred to the patient or frozen for future use. It is often used interchangeably with the term “IVF Lab”.

Embryo Transfer:  The process of placing embryos into the uterus that have been grown in the IVF lab.  These embryos are gently aspirated into a soft catheter by an embryologist and then handed to a physician.  The physician passes the catheter through the cervix of the intended mother to a pre-determined depth into the uterine cavity.  The embryos are then gently expelled into the uterus and the catheter is removed.

Endometrium – the lining of the uterus. The endometrium grows a thick, blood-vessel rich layer during the mid-estrous cycle allowing for an optimal environment for the implantation of the embryo.

Estrogen – a steroid hormone produced by the ovarian follicles. One of the functions of estrogen is stimulation of endometrial growth.

Fallopian Tubes:  The tubes that transport the egg from the ovary of a woman to her uterus.  These “oviducts” are also the site where sperm from the male partner fertilize the egg in the body.

Fertilization – The method by which an oocyte and a sperm combine for form an embryo. In IVF, successful fertilization is detected by the presence of 2 pronuclei (one from the sperm and one from the oocyte).

Follicle – The ovarian structure in which oocytes develop and mature.

Gene – A unit of heredity. A gene is a location on a chromosome and codes for a protein or strand of RNA. Genes hold information that codes for heritable genetic traits.

Germinal Vesicle (GV) – The nucleus of an oocyte prior to meiosis and the reduction of the chromosome number. The presence of a GV is indicative of an immature oocyte.

hCG – (human chorionic gonadotropin) – a protein hormone produced by a developing embryo. Detection of the presence of this hormone is used in early pregnancy tests. hCG is also used as an ovulation inducer. The injection of hCG triggers the large follicles to finish maturation and to ovulate within 38-40 hours.

Incubator:  The chambers where embryos are kept while they are growing in the laboratory.  These chambers provide conditions that mimic those experienced by the embryos when they are developing in the body.  The temperature, pH and gas concentration of oxygen, carbon dioxide and nitrogen are all controlled in the same manner as they are in the Fallopian tubes and in the uterus.

Inner Cell Mass (ICM) – A small grouping of cells in the blastocyst stage embryo. The ICM will develop into the fetus.

Insemination:  The placement of sperm in a dish containing eggs for the purpose of fertilizing the eggs.  Usually several thousand sperm are placed in a drop of culture medium with one to three eggs for up to 18 hours.

Intra-cytoplasmic Sperm Injection (ICSI):  The injection of a single sperm into an egg for the purpose of accomplishing fertilization.  This is done in the place of insemination in the IVF lab when the sperm has one or more problems that might significantly reduce the chances of fertilization.

Intrauterine Insemination (IUI):  The injection of sperm into the uterus after they have been washed free of semen and re-suspended in a nutrient solution.

In Vitro Fertilization (IVF):  The formation and growth of embryos in a laboratory after eggs and sperm have been combined with the purpose of transferring healthy embryos into the uterus of the intended mother.

Laser:  A beam of light at a certain wavelength that can be used in the IVF process to create a hole in the shell of an embryo.  This process is known as assisted hatching and is used to facilitate an embryo breaking free of its shell prior to implanting on the uterine lining.    

Liquid Nitrogen:  The fluid that is used to store cryopreserved eggs, sperm and embryos while in the frozen state in the laboratory.  This liquid is kept in storage units that are independent of electrical power.  The nature of the extreme cold temperature of the liquid nitrogen (-320 degrees Fahrenheit) allows cells to be kept in a state of suspended animation for many years.

Luteinizing Hormone (LH):  The hormone that is produced by the follicles of the ovaries around the time of ovulation.  A rise in the level of this hormone in the urine or serum of a woman is an indicator that ovulation is very close.  Patients who want to time ovulation for the purpose of replacing thawed embryos with a natural cycle will monitor their LH level.

Metabolism:  The taking in and breaking down of nutrients contained in the environment by living cells.  This process results in the growth, maturation and division of these cells into new cells.  This is the process by which embryos and all living cells continue to grow.

Morula – The embryo stage after the multi-cell stage. In this stage the embryo is a compact ball of cells. It is difficult to distinguish individual cells at this stage as they are so compacted together.

Multi-cell Embryo – A cleavage stage embryo. At this stage the embryo increases in cell number without increasing the overall size of the embryo. An embryo is at the multi-cell stage from day 2 until day 4 when it develops into a morula.

Mutation – Change in a DNA sequence. A mutation can have a favorable, a detrimental or no effect on an organism.

Oocyte – An egg.  The cells that are formed in the follicles of the ovaries.  These are the cells that contain the genetic material of the mother.

Oocyte Retrieval – The method by which oocytes are removed from a patient’s ovaries. An ultrasound transducer with a needle guide is inserted into the vagina and is used to visualize the ovaries. As the follicles within the ovaries are visualized, a needle is advanced through the vaginal wall into the follicles. The follicular fluid and egg are aspirated from each follicle.

Organelles:  The structures within cells that carry out all of the life functions of the cells.  One example is mitochondria.  These are energy factories within the cells that take the nutrients that have passed into the cells from the environment and turn them into energy sources.  The energy created by the mitochondria allows the cell to carry on all of its other functions.

Ovulation – The process in which an ovarian follicle ruptures and expels the oocyte contained within that follicle.

Preimplantation Genetic Diagnosis (PGD) – The testing of embryos for specific inherited genetic diseases.

Preimplantation Genetic Screening (PGS) – The testing of embryos to determine if they carry the proper number of chromosomes.

Polar body – A small, round body located on the side of the egg that contains half of the chromosomes from the egg. This is produced during oocyte maturation and is the result of the oocyte undergoing meiosis in order to reduce the number of chromosomes present in the oocyte. This is necessary prior to the introduction of a sperm in order for the embryo to have the proper number of chromosomes. The presence of the first polar body is an indication that an oocyte is mature and receptive to penetration by a sperm. The presence of a second polar body is sometimes an indication of fertilization and a signal that meiosis is complete.

Polygynic  An oocyte containing more than two pronuclei. In this case, the extra pronucleus(i) is due to the oocyte undergoing incomplete meiosis.

Polyploid – The presence of more than two pronuclei within an oocyte. The extra pronucleus(i) can either be from the oocyte undergoing incomplete meiosis, or from extra sperm entering the oocyte.

Polyspermic – An oocyte containing more than two pronuclei. In this case, the extra pronucleus(i) is due to more than one sperm entering the oocyte.

Pronucleus – The nucleus of a sperm or an oocyte within the cytoplasm of the oocyte. The development of two pronuclei within an oocyte after exposure to sperm signals successful fertilization. Each pronucleus is haploid or contains half the number of chromosomes needed by the embryo.  The pronuclei will fuse and the chromosomes will combine to form an embryo with a single diploid nucleus.

Semen:  The liquid products of the prostate gland and the seminal vesicles that is ejaculated from the penis during sexual intercourse or masturbation.  It contains sperm for the purpose of fertilizing eggs.  It is also known as seminal plasma.

Semen Analysis:  The examination of semen samples to determine the volume and the sperm count, motility, progression and morphology.

Sequential Culture Media:  The media that are used in the in vitro fertilization process to support embryo growth while the embryos are in the lab.  These media mimic the nutrients that are located in the different areas of the reproductive tract of the woman.

Sperm:  The cells that are formed in the testes and are contained within the fluids of the prostate gland and the seminal vesicles during ejaculation.  They are the cells that contain the genetic material of the father.  Their purpose is to fertilize the egg(s) of the intended mother.  Their tails propel them through the cervix of a woman, across the cavity of the uterus and into the Fallopian tubes where fertilization of the egg occurs in the body.

Trophectoderm – A layer of cells that surrounds the ICM and the blastocoel in a blastocyst stage embryo. The trophectoderm will later form the placenta.

Uterus:  The organ that is the site of embryo implantation and growth of the fetus to term.  It is the site of the placement of the embryo transfer catheter by the physician during the post IVF embryo transfer. 

Zona Pellucida – A glycoprotein membrane surrounding the plasma membrane of an oocyte. This “shell” around the oocyte binds sperm and is required for normal fertilization. The zona pellucida remains around the embryo until it develops into an expanded Blastocyst at which time the embryo “hatches”.

Zygote – a fertilized oocyte containing two pronuclei.

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