Blastocyst Health Dictionary

Fertilisation of the egg (ovum) outside the body. The fertilised ovum is then incubated until the blastocyst stage develops, when it is implanted into the UTERUS. The procedure was developed in Britain and the ?rst successful in vitro baby, a girl, was born in 1978. IVF is used when a woman has blocked FALLOPIAN TUBES or when the sperm and ovum are unable to fuse in the reproductive tract. Hormone treatment results in the potential mother’s producing several mature ova, some of which are removed from the ovary using a LAPAROSCOPE and fertilised with her partner’s semen. (See ASSISTED CONCEPTION.)... in vitro fertilisation (ivf)

The fertilization of a woman’s ovum by a man’s sperm, followed by implantation of the resultant blastocyst in the lining of the uterus thus starting a pregnancy. (See also contraception.)... conception

Attachment of a fertilized ovum (egg) to the wall of the uterus.

It occurs about 6 days after fertilization, when the blastocyst (early embryo) comes into contact with the wall of the uterus.

As the cells of the developing embryo continue to divide, the outer cell layer penetrates the lining of the uterus to obtain oxygen and nutrients from the mother’s blood; later, this layer develops into the placenta.

The embryo usually implants in the upper part of the uterus; if it implants low down near the cervix, placenta praevia may develop.

Rarely, implantation occurs outside the uterus, possibly in a fallopian tube, resulting in an ectopic pregnancy.... implantation, egg

The cell that is produced when a sperm fertilizes an ovum. A zygote, measuring about 0.1 mm in diameter in humans, contains all the genetic material for a new individual. The zygote is surrounded by a protein-rich layer known as the zona pellucida.

The zygote travels down 1 of the woman’s fallopian tubes, dividing as it does so. After about a week, the mass of cells (now called a blastocyst) implants into the lining of the uterus, and the next stage of embryological growth begins.

(See also embryo; fertilization.)... zygote

the fluid-filled cavity between the embryo and the *amnion. It forms initially within the inner cell mass of the *blastocyst and later expands over the back of the embryo, eventually enclosing it completely. See also amniotic fluid.... amniotic cavity

n. the fluid-filled cavity that develops within the *blastocyst. The cavity increases the surface area of the embryo and thus improves its ability to absorb nutrients and oxygen.... blastocoele

n. any of the cells produced by *cleavage of the zygote, comprising the earliest stages of embryonic development until the formation of the *blastocyst. Blastomeres divide repeatedly without growth and so decrease in size.... blastomere

n. an early stage of the embryonic development of many animals. The equivalent stage in mammals (including humans) is the *blastocyst.... blastula

n. (in embryology) the process of repeated cell division of the fertilized egg to form a ball of cells that becomes the *blastocyst. The cells (blastomeres) do not grow between divisions and so they decrease in size.... cleavage

n. the process of making identical copies (*clones) of genes, cells, or organisms. Therapeutic cloning, which is lawful if licensed by the Human Fertilisation and Embryology Authority, produces human blastocysts to harvest their *stem cells. In reproductive cloning, whole animals are produced: see clone (sense 2); reproductive cloning of humans is unlawful in the UK. The moral issues relative to therapeutic and reproductive cloning are hotly debated, although for many it is the purpose of cloning that determines its moral acceptability or otherwise.... cloning

combining form denoting 1. a body cavity. Example: blastocoele (cavity of blastocyst). 2. see -cele.... coele

(fetal graft) the introduction of an ovum, fertilized in vitro and developed to the *blastocyst stage, into the uterus of a postmenopausal woman in order that she may become pregnant. Before this procedure, the woman’s uterus must be prepared, by hormone therapy, to receive and nurture the blastocyst. Hormone treatment is continued throughout the pregnancy.... fetal implant

n. 1. (nidation) the attachment of the early embryo to the lining of the uterus, which occurs at the *blastocyst stage of development, six to eight days after ovulation. The site of implantation determines the position of the placenta. 2. the placing of a substance (e.g. a drug) or an object (e.g. an artificial pacemaker) within a tissue. 3. the surgical replacement of damaged tissue with healthy tissue (see transplantation).... implantation

n. an early stage of embryonic development formed by *cleavage of the fertilized ovum. It consists of a solid ball of cells and is an intermediate stage between the zygote and *blastocyst.... morula

(Suzi) a method of assisting conception in cases of infertility caused by the inability of the spermatozoa to penetrate the barriers surrounding the ovum. Using *in vitro fertilization techniques, a small number of spermatozoa (no more than six) are injected through the *zona pellucida into the perivitelline space (which surrounds the egg membrane). If fertilization subsequently occurs, the blastocyst is implanted in the mother’s uterus.... subzonal insemination

(IVF) fertilization of an ovum outside the body, the resultant *zygote being incubated to the *blastocyst stage and then implanted in the uterus. The technique, pioneered in Britain, resulted in 1978 in the birth of the first test-tube baby. IVF may be undertaken when a woman has blocked Fallopian tubes, unexplained infertility, endometriosis, or ovulation disorders; it is also carried out for purposes of surrogacy and egg donation. The mother-to-be is given hormone therapy causing a number of ova to mature at the same time (see superovulation). Several of them are then removed from the ovary through a laparoscope. The ova are mixed with spermatozoa and incubated in a culture medium until the blastocyst is formed. The blastocyst is then implanted in the mother’s uterus and the pregnancy proceeds normally. IVF is regulated by the *Human Fertilisation and Embryology Act 1990 via the Human Fertilisation and Embryology Authority.... in vitro fertilization

(PGD) a diagnostic procedure carried out on embryos at the earliest stage of development, before implantation in the uterus. Access to these early embryos requires the *in vitro fertilization of egg cells: three days after fertilization one or two cells are aspirated from the six-cell embryo; alternatively, tissue is removed from an embryo at five or six days, when it has reached the *blastocyst stage. Isolated cells can then be genetically analysed, allowing the transfer of selected embryos to the mother. One of the major applications of PGD is for the detection (using the *FISH technique) of chromosomal abnormalities, especially *aneuploidies (e.g. Down’s syndrome); the procedure is used mainly in women who have had repeated miscarriages or have failed to achieve pregnancy after several IVF treatment cycles, which could be due to the presence of such abnormalities in the embryo. PGD can also be used to detect defective genes responsible for hereditary disorders (e.g. the commonest form of cystic fibrosis, Huntington’s disease) and genes associated with susceptibility to certain cancers. When a defect is detected, *genetic counselling is offered.... preimplantation genetic diagnosis

an undifferentiated cell that is able to renew itself and produce specialized cells. Embryonic stem cells at the *blastocyst stage of development can differentiate into almost any cell type (except placental cells); they are described as pluripotent. Embryonic cells preceding the blastocyst, produced by the first 3–4 divisions of the fertilized egg, are capable of producing all the different cell types required by the developing embryo (i.e. they are totipotent). Adult stem cells (also known as somatic stem cells) occur in many tissues and organs, including bone marrow (see haemopoietic stem cell), muscle, liver, pancreas, etc., and can produce the specialized cells needed in the particular tissue or organ in which they arise (i.e. they are multipotent). See also umbilical cord blood banked stem cells.... stem cell

n. the tissue that forms the wall of the *blastocyst. At implantation it forms two layers, an inner cellular layer (cytotrophoblast), which does not invade maternal tissue and forms the outer surface of the *chorion; and an outer syncytial layer (syncytiotrophoblast, or plasmoditrophoblast), which erodes the maternal tissue and forms the chorionic *villi of the placenta. See also gestational trophoblastic disease.... trophoblast

the thick membrane that develops around the mammalian oocyte within the ovarian follicle. It is penetrated by at least one spermatozoon at fertilization and persists around the *blastocyst until it reaches the uterus. See ovum.... zona pellucida