China
Africa
Explore chapters and articles related to this topic
In Vitro Fertilization and Embryo Transfer
Published in Asim Kurjak, Ultrasound and Infertility, 2020
The mature oocyte is normally found surrounded with transparent cumulus and in highly stretchable intercellular substance. The border of the oocyte, as well as zones pellucida, are clearly distinguishable. Granulosa cells, with characteristic abundant cytoplasm, are found all around the oocyte. Meiotic changes in the mature egg are already completed, and the polar body is expelled out of the cell.
Preimplantation Genetic Testing for Aneuploidies: Where We Are and Where We're Going
Published in Darren K. Griffin, Gary L. Harton, Preimplantation Genetic Testing, 2020
Andrea Victor, Cagri Ogur, Alan Thornhill, Darren K. Griffin
Polar body (PB) biopsy was first introduced to identify oocytes that carry disease alleles in women heterozygous for a genetic disease [20]. Polar bodies are the byproducts of meiosis I and II, and their biopsy is not likely to impact negatively on an embryo's future development. Polar bodies may be removed either one at a time or simultaneously following fertilization [21], but because they might undergo rapid fragmentation, any delay in biopsy could result in misdiagnosis or no result. The primary advantages of polar body biopsy are that it is less invasive than other forms and it inherently creates a greater time window for analysis when performing transfer for a fresh cycle. Disadvantages lie in the fact that polar bodies cannot be used to detect paternal chromosomes or post-zygotic errors. Consequently, polar body biopsy is limited in PGT-A to the diagnosis of meiotic abnormalities and translocations of maternal origin. Polar body biopsy gained popularity when it was proposed as an alternative to cleavage-stage biopsy [22,23], which, after randomized controlled trials (RCTs) [15,24] , limited the applicability of PGT-A. Indeed, the first successful live birth following 24-chromosome screening was performed following polar body biopsy [25].
Regulation of Reproduction by Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The resumption of meiosis (oocyte maturation) is triggered by the preovulatory LH surge. The meiotic block is removed and the primary oocyte completes the first meiotic division. An asymmetric cytoplasmic division generates a large secondary oocyte and a small discarded cell, called the polar body. The secondary oocyte then enters meiosis II and becomes arrested at metaphase II. The resumption of meiosis at the time of ovulation is characterized by the dissolution of the nucleus, commonly referred to as germinal vesicle breakdown (GVBD). After GVBD, the chromatin is condensed into chromosomes, microtubules are organized into meiotic spindles, and the homologous chromosomes are separated to emit the first polar body. The post-GVBD maturational processes are controlled by histone modifications, centrosome proteins, various protein kinases/phosphatases, spindle checkpoints, and cytoskeletons.
Aluminum reproductive toxicity: a summary and interpretation of scientific reports
Published in Critical Reviews in Toxicology, 2020
The development of an oocyte begins as a primordial germ cell. Early in embryonic development these cells migrate into the future site of the ovaries, undergo meiotic cell division, and multiply, resulting in primary oocytes (primordial follicle) within the ovary. Their development is arrested until puberty, when follicle stimulating hormone (FSH) produced by the pituitary gland stimulates some to begin to mature, developing through follicle stages (primary, secondary, and if fertilized tertiary (Graafian) follicles), in the process of folliculogenesis. Most die (atresia) during these stages. During the resumption of cell division, the oocyte’s nucleus (germinal vesicle) breaks down and the first polar body (that forms concomitantly during oocyte division) is extruded. Follicle cells secrete and release estrogen that feeds back to the pituitary gland to decrease FSH release and increase luteinizing hormone (LH) release. This causes the follicle to rupture, resulting in release of the egg (ovulation), that migrates into the fallopian tubes where it can be fertilized by sperm. The ruptured follicle forms a corpus luteum, a transitory endocrine organ that secretes estrogen and progesterone. The latter feeds back to the pituitary gland to decrease LH release. The fertilized oocyte forms a mature egg cell (ovum). When the oocyte and sperm chromosomes combine, it becomes a zygote, which divides as it migrates into the uterus, creating the pregnant (gravid) state.
Levels of total antioxidant capacity and 8-hydroxy-2′-deoxyguanosine of serum and follicular fluid in women undergoing in vitro fertilization: focusing on endometriosis
Published in Human Fertility, 2020
Ákos Várnagy, Tamás Kőszegi, Erzséber Györgyi, Sarolta Szegedi, Endre Sulyok, Viktória Prémusz, József Bódis
We performed the fertilization with intracytoplasmatic sperm injection (ICSI) depending on the andrological status (sperm count less than 15M/ml), the maternal age (>35) and the number of the previous IVF cycles the patient had undergone previously (>2). The oocytes selected for ICSI were denuded with hyaluronidase and were assessed for maturity. Only metaphase II oocytes, identified by the presence of the first polar body, were chosen for fertilization. ICSI was performed 3–6 h after oocyte recovery in the medium G-MOPS™. The remained oocytes were fertilized with the conventional IVF method in a bicarbonate-buffered medium (G-IVF™, Vitrolife®, Göteborg, Sweden). Fertilization was assessed 24 hours later in the medium G-I™v5 (Vitrolife®, Göteborg, Sweden).
Cryopreservation of human embryos and oocytes for fertility preservation in cancer and non cancer patients: a mini review
Published in Gynecological Endocrinology, 2020
Oocyte cryopreservation at a young age would anticipate the detrimental effects of the reduced ovarian reserve and would allow the storage of a high number of oocytes. Despite cryopreservation of immature oocytes and in vitro maturation is a promising option is still considered experimental [74] therefore in this section will be only discussed cryopreservation of mature oocyte (MII). At this stage, both nuclear and cytoplasmic maturations have occurred, the first polar body has been extruded and the chromosomes are condensed and arranged on the meiotic spindle. Beyond the more common event of oolemma breakage and consequent oocyte degeneration as a direct effect of physical damage due to intracellular ice formation or osmotic stress, the process of cryopreservation may entail several hidden alterations of oocyte physiology. Possible injuries of the oocyte integrity, resulting from cooling and warming, might be represented by ZP hardening [38], damage to the meiotic spindle [34–37], DNA fragmentation [75], damage to intracellular organelles [76] and epigenetic risks [77].