ABB Embryology key terms

The process by which diploid germ cells undergo meiosis and maturation to form haploid sperm or oocytes, including the cytoplasmic and structural changes that prepare them for fertilization.

A two-stage cell division that halves chromosome number, producing haploid gametes and generating genetic variation through crossing over and independent assortment of homologous chromosomes.

The continuous, testosterone-driven maturation of spermatogonia into spermatozoa within the seminiferous tubules, involving mitotic proliferation, meiotic division, and spermiogenesis.

The final maturation phase of spermatogenesis in which round spermatids develop a tail, acrosome, and condensed nucleus to become motile spermatozoa, without further cell division.

The development of oocytes from oogonia, beginning before birth and arrested in prophase I until ovulation, when meiosis resumes and completes only after fertilization.

Describing a cell or nucleus containing a single set of chromosomes, as in mature sperm and oocytes, contrasting with the diploid chromosome complement of somatic cells.

A cap-like vesicle at the sperm head containing hydrolytic enzymes that, after the acrosome reaction, help digest the zona pellucida and allow sperm penetration during fertilization.

The mature male gamete, comprising a head with condensed nucleus and acrosome, a midpiece rich in mitochondria, and a flagellar tail that provides motility.

A small byproduct cell cast off during oocyte meiotic divisions, containing chromosomes but minimal cytoplasm, allowing the oocyte to retain nutrients while reducing chromosome number.

The fusion of a sperm and oocyte, triggering completion of meiosis, formation of the zygote, and initiation of embryonic development.

The calcium-dependent release of acrosomal enzymes after sperm bind the zona pellucida, enabling penetration of the egg coat and fusion with the oocyte membrane.

A glycoprotein coat surrounding the oocyte that mediates sperm binding, blocks polyspermy after fertilization, and must be escaped by the embryo before implantation.

The haploid nucleus of a sperm or oocyte after gamete fusion but before the first mitotic division; the appearance of two pronuclei confirms successful fertilization.

The final union of maternal and paternal pronuclear genetic material to form the diploid zygote genome, marking the end of fertilization.

The single diploid cell formed when sperm and oocyte fuse, representing the beginning of a new embryo and the starting point of cleavage divisions.

A series of rapid mitotic divisions of the zygote that increase cell number without increasing overall embryo volume, producing progressively smaller blastomeres.

An individual cell produced by cleavage of the early embryo; blastomere number and symmetry are key parameters in embryo grading.

The process around the morula stage in which blastomeres flatten and adhere tightly, forming a compact mass and establishing the outer cell layer that will become the trophectoderm.

A compacted embryo of roughly 16 to 32 cells, formed after several cleavage divisions, that precedes formation of the fluid-filled blastocyst cavity.

A fluid-filled embryo stage with an outer trophectoderm, an inner cell mass, and a blastocoel cavity, typically reached about five to six days after fertilization.

The cluster of pluripotent cells inside the blastocyst that gives rise to the embryo proper, and whose size and organization contribute to blastocyst grading.

The outer epithelial cell layer of the blastocyst that mediates implantation and later forms placental tissues; its cell count and uniformity are assessed during blastocyst grading.

The escape of the blastocyst from the zona pellucida, a prerequisite for implantation that can be assisted by creating a small opening in the zona.

The ultrasound-guided transvaginal aspiration of mature follicles to collect oocytes, typically performed under sedation and timed about 34 to 36 hours after ovulation trigger.

The enzymatic and mechanical removal of cumulus and corona cells from retrieved oocytes to allow clear visualization of the oocyte for maturity assessment and micromanipulation.

The developmental stage of a retrieved oocyte, judged by the presence of a first polar body (metaphase II) or a germinal vesicle (immature), determining suitability for insemination or injection.

A micromanipulation technique in which a single selected sperm is injected directly into the cytoplasm of a mature oocyte to achieve fertilization.

The use of precision-controlled glass tools and motorized microinjectors under a microscope to manipulate gametes and embryos, as in sperm injection, biopsy, or assisted hatching.

A micromanipulation procedure that weakens or opens the zona pellucida, by laser, acid, or mechanical means, to help the blastocyst escape before implantation.

The removal of one or more cells from an embryo, usually trophectoderm cells at the blastocyst stage, for genetic testing while preserving embryo viability.

The laboratory process of choosing the most suitable sperm for injection or insemination based on motility, morphology, and viability, sometimes aided by specialized techniques.

A formulated solution supplying salts, energy substrates, amino acids, and proteins that supports gamete handling and embryo development in vitro under controlled conditions.

A controlled chamber maintaining temperature, humidity, and gas concentrations to support embryo development outside the body, typically held near 37 degrees Celsius.

A gas supplied to incubators at around five to six percent to maintain the bicarbonate buffer system and stable pH of embryo culture medium.

The concentration of dissolved particles in a medium, which influences water movement across cell membranes and must be controlled to avoid osmotic stress on gametes and embryos.

The maintenance of embryos in vitro from fertilization to transfer or freezing, using appropriate media, gas atmosphere, temperature, and handling to support normal development.

An ultra-rapid cryopreservation method that converts cells and surrounding solution into a glass-like solid without ice crystal formation, preserving gametes and embryos.

A solute such as glycerol or dimethyl sulfoxide added before freezing to reduce ice formation and cellular dehydration injury during cooling and warming.

A controlled-rate cryopreservation method that cools samples gradually with seeding to manage ice formation, largely replaced by vitrification for oocytes and blastocysts.

The controlled thawing of vitrified or frozen samples in stepwise solutions that remove cryoprotectant and restore cells to physiological conditions.

Microscopic evaluation after thawing to determine whether gametes or embryos have retained membrane integrity and structural features, guiding decisions on clinical use.

A standardized morphological scoring of cleavage-stage or blastocyst embryos based on cell number, symmetry, fragmentation, and development to guide selection for transfer or freezing.

A scoring system that evaluates blastocyst expansion, inner cell mass quality, and trophectoderm quality to rank embryos by implantation potential.

The presence of small extracellular cytoplasmic fragments within a cleavage-stage embryo, scored as a percentage of embryo volume and associated with reduced viability.

Continuous automated monitoring of embryo development in the incubator, capturing morphokinetic events to support selection without disturbing culture conditions.

The process of choosing which embryo to transfer or cryopreserve, based on morphology, developmental timing, genetic testing, and other laboratory and clinical information.

The set of routine laboratory measures, such as equipment monitoring, media testing, and assay checks, that verifies procedures meet defined performance standards.

The broader management system of policies, audits, and reviews that ensures the laboratory consistently delivers reliable results and meets regulatory and accreditation requirements.

The control of particulates and volatile organic compounds in the laboratory environment through filtration and ventilation, protecting gametes and embryos from toxic exposure.

Continuous measurement and documentation of incubator, warming block, and storage temperatures to detect deviations that could compromise gametes or embryos.

The documented ability to track each sample, reagent, and procedure through unique identifiers from collection to outcome, supporting safety, audits, and error investigation.

The maintenance of frozen gametes and embryos in liquid nitrogen or vapor tanks with identity checks, temperature alarms, and inventory records to prevent loss or mix-up.

The documented, voluntary agreement of patients to a procedure or use of their gametes and embryos, given after receiving adequate information about risks and options.

The provision of sperm or oocytes by a third party for treatment, governed by screening, anonymity, consent, and compensation rules set by local regulation.

The agreed use or fate of cryopreserved embryos, such as transfer, donation to research or another person, or disposal, determined by patient consent and regulation.

Genetic analysis of biopsied embryo cells to detect chromosomal or single-gene abnormalities before transfer, informing embryo selection.

The presence of two or more genetically distinct cell lines within one embryo, which complicates interpretation of genetic test results and transfer decisions.

Formal recognition by an external body that a laboratory meets defined standards for competence, safety, and quality management, often required for clinical practice.