Great obstetrical syndromes
Moshe Hod, Vincenzo Berghella, Mary E. D'Alton, Gian Carlo Di Renzo, Eduard Gratacós, Vassilios Fanos in New Technologies and Perinatal Medicine, 2019
In human pregnancy, embryo implantation is initiated by apposition of the blastocyst with its embryonic pole, bearing the inner cell mass, to the endometrial epithelium. While the inner cell mass gives rise to the embryo, the outer cell mass—referred to as trophoblast cells—forms the wall of the blastocyst, thus mediating initial adherence to the uterine wall and later forming the placenta. Apposition and adherence of the blastocyst are followed by intercellular fusion of trophoblasts that are in contact with the endometrial epithelium, to form the multinucleated syncytiotrophoblast (9). At that very early stage of embryo implantation, the syncytiotrophoblast is equipped with an enzymatic endowment that enables crossing of the endometrial epithelium and penetration of the underlying stroma. The endometrium from now on may be referred to as decidua, which provides the breeding ground for the growing embryo and the developing placenta. Once the blastocyst has completely penetrated the decidua, the mass of syncytiotrophoblast rapidly increases by ongoing proliferation and fusion of underlying cytotrophoblasts. The syncytiotrophoblast forms a complete layer over the surface of the blastocyst, whereas the site at the implantation pole achieves considerable thickness and develops extensions that deeply invade the decidua.
Epigenetic considerations in preimplantation mammalian embryos
David K. Gardner, Ariel Weissman, Colin M. Howles, Zeev Shoham in Textbook of Assisted Reproductive Techniques, 2017
Mammalian oocytes are arrested at the germinal vesicle (GV) stage in the ovary at birth and remain at this stage until puberty. Follicle-stimulating hormone induces development of small antral follicles, resulting in one oocyte and its follicle becoming ovulatory. Meiotic resumption occurs after GV breakdown induced by luteinizing hormone and starting the process of oocyte maturation. Growth of the oocyte is associated with significant remodeling on cellular and molecular levels, resulting in the oocyte becoming fertilization-competent (reviewed in [2-12]). The first meiotic spindle forms, followed by second meiosis, during which the oocyte becomes arrested at metaphase II (MII) to await fertilization in order for development to continue. The meiotic stages encompass two successive, highly asymmetric cell divisions that result in small polar bodies and a large polarized oocyte. Fertilization after sperm incorporation triggers egg activation and formation of one male and one female pronucleus (zygote stage, day 1 in humans) that become appositioned and undergo chromosomal reorganizations before the mitotic spindle forms and separates chromosomes equally to the dividing daughter cells. Cell divisions continue, and at the eightcell stage (day 3), embryos start to undergo compaction, a process during which the blastomeres become flattened and polarized. Blastocyst development continues with cellular differentiation when inner cells are formed (day 5; 32-cell stage) resulting in the inner cell mass (ICM) cells and the outer cells that form the trophectoderm (TE).
Stem Cells
John C Watkinson, Raymond W Clarke, Louise Jayne Clark, Adam J Donne, R James A England, Hisham M Mehanna, Gerald William McGarry, Sean Carrie in Basic Sciences Endocrine Surgery Rhinology, 2018
About 20 years ago, it was discovered that cells of the inner cell mass of mouse blastocysts, the cells that would normally go on to form the embryo, can be isolated, greatly expanded in vitro and then differentiated into multiple cell lineages.4 Such ‘embryonic stem cells’ (ES cells) were later also derived from human blastocysts. The controlled in vitro differentiation of ES cells into a required cell type can be directed using signals that mimic the tissue interactions that guide emergence of regionally appropriate cell lineages during embryonic development. Consequently, ES cells can provide an essentially unlimited source of relevantly differentiated cells.4 However, ES cells are generated by destruction of living human blastocysts and strong opposition to the use of ES cells has been expressed on ethical grounds. A further major complexity is that tissues produced from ES cells express the histocompatibility antigens genetically determined by the donor embryo and, consequently, their compatibility with recipients is restricted to some immune-privileged sites, requires manipulation of the recipient’s immune system, or modification of antigens expressed by the stem cell.
Preimplantation genetic diagnosis (PGD) and genetic testing for aneuploidy (PGT-A): status and future challenges
Published in Gynecological Endocrinology, 2020
Romualdo Sciorio, Luca Tramontano, James Catt
In the late 1990s, it became standard practice to extend embryo culture up to the blastocyst stage [30]. At this point, the embryo is already differentiated into two distinct cell types: the inner-cell mass (ICM) that will develop and form the fetus, and the trophectoderm (TE) cells which will become the placenta. As mentioned earlier, in recent times, many IVF units have left cleavage stage biopsy, and have turned to TEB as this biopsy offers some advantages. First, 5-10 cells can be biopsied from the blastocyst and this makes the genetic diagnosis more reliable and less prone to errors [31,32]. Second, TEB is believed to have a smaller detrimental effect on embryo viability compared to biopsy on day-3. Finally, TE biopsy reduced the risk of mosaicism [25]. To perform TEB, it is required to make a hole in the ZP either on day-3 or on day-5, and to wait for the beginning of TE herniation, which represents the optimal time to start the biopsy. Recently, the biopsy of blastocoel fluid has been proposed by Palini et al. [33] as new source of embryonic genetic material (Figure 2). With the introduction of vitrification as a highly efficient cryopreservation method, it is possible to combine blastocyst biopsy with vitrification and genetic screening, followed by warming and transfer of euploid embryos in a subsequent cycle [34,35].
A comparison of the survival and implantation rates of blastocysts that were vitrified on post-fertilization day five, six and seven
Published in Human Fertility, 2019
Avci Berrin, Kasapoglu Isıl, Ata Baris, Kuspinar Goktan, Saribal Seda, Uncu Gurkan
Gardner’s classification was used to assess blastocysts before vitrification (Gardner & Schoolcraft, 1999). Briefly, expansion status was graded as follows: grade 1 early blastocyst; grade 2 blastocyst; grade 3 full blastocyst; grade 4 expanded blastocyst; grade 5 hatching blastocyst; and grade 6 hatched blastocyst. The inner cell mass (ICM) was graded as follows: (A) tightly packed many cells; (B) loosely packed cells; and (C) dispersed few cells. The trophectoderm (TE) was graded as follows: (A) many cells forming a cohesive epithelium; (B) few cells forming a loose epithelium; and (C) very few large cells. Surplus blastocysts were vitrified if and when they reached expanded blastocyst stage (i.e. grade 3 or above, on post fertilization days 5, 6 or 7). The day of vitrification was not arbitrarily determined due to staff availability or weekends.
Cleavage-stage embryo micromanipulation in the clinical setting
Published in Systems Biology in Reproductive Medicine, 2018
Iman Halvaei, Shahin Ghazali, Stefania A. Nottola, Mohammad Ali Khalili
ZP hatching is a natural process caused by serine proteases released from maternal (uterine cells) or embryonic (trophectoderm cells) sources or/and increasing internal pressure due to blastocyst expansion (Cohen 1991; O’Sullivan et al. 2002; Sathananthan et al. 2003). Normally, the embryo escapes from the ZP 5–6 days after fertilization just before implantation. There are some factors that impair hatching, including abnormality in ZP structure, increase in ZP thickness, and zona hardening. Advanced maternal age, ovarian stimulation protocol, sub-optimal in vitro culture and cryopreservation may induce zona hardening (Aston and Weimer 2010). Assisted hatching (AH), by creating an opening in the ZP, helps the embryo to escape from the ZP. In human embryos, the site of hatching is in close proximity to the blastocyst inner cell mass (Gonzales et al. 1996). Therefore, the site of AH seems important for the initiation of hatching (Miyata et al. 2010). The recommended indications for AH include advanced maternal age (≥40 years), elevated FSH level, thick ZP (>15µm), frozen-thawed embryos, and history of implantation failure (≥2) (Cohen et al. 1992; Schoolcraft et al. 1994; Tao and Tamis 1997; Mansour et al. 2000; Hammadeh et al. 2011). Some AH indications are referred to in vitro culture like zona hardening or lack of produced protease by the embryo (Schiewe et al. 1995). Recently, Razi et al. (2013) in a prospective randomized study evaluated the ART outcomes following laser AH (LAH) in patients undergoing their first ICSI treatment due to male factor infertility. They showed that the clinical pregnancy and the live birth rates were similar between patients with AH and the control group (Razi et al. 2013).
Related Knowledge Centers
- Fetus
- Implantation
- Embryo
- Trophoblast
- Endometrium
- Uterus
- Pluriblast
- Blastocyst
- Animal Embryonic Development
- Cleavage