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Implantation, also known as nidation, [1] is the stage in the mammalian embryonic development in which the blastocyst hatches, attaches, adheres, and invades into the endometrium of the female's uterus. [2] Implantation is the first stage of gestation, and, when successful, the female is considered to be pregnant. [3]
In 1965, the American College of Obstetricians and Gynecologists (ACOG) adopted Boving's definition: "conception is the implantation of a fertilized ovum." [ 25 ] The 1965 ACOG definition was imprecise because, by the time it implants, the embryo is called a blastocyst , [ 26 ] so it was clarified in 1972 to "Conception is the implantation of ...
The implantation is assisted by hydrolytic enzymes that erode the epithelium. The syncytiotrophoblast also produces human chorionic gonadotropin, a hormone that stimulates the release of progesterone from the corpus luteum. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can oxygenate and sustain ...
On average, implantation occurs about 8-10 days after ovulation, but it can happen as early as six and as late as 12. This means that for some women, implantation can occur around cycle day 20 ...
There is also considerable variability in this interval, with a 95% prediction interval of the ovulation of 9 to 20 days after menstruation even for an average woman who has a mean LMP-to-ovulation time of 14.6. [32] In a reference group representing all women, the 95% prediction interval of the LMP-to-ovulation is 8.2 to 20.5 days. [31]
The term "conception" refers variably to either fertilization or to formation of the conceptus after its implantation in the uterus, and this terminology is controversial. The zygote will develop into a male if the egg is fertilized by a sperm that carries a Y chromosome, or a female if the sperm carries an X chromosome. [5]
The term conception commonly refers to "the process of becoming pregnant involving fertilisation or implantation or both". [32] Its use makes it a subject of semantic arguments about the beginning of pregnancy , typically in the context of the abortion debate.
The embryo hatches from its protein shell (zona pellucida) and performs implantation onto the endometrial lining of the mother's uterus. (day 5–6 of fertilization. [1]) If separation into identical twins occurs, 1/3 of the time it will happen before day 5. [2]