Title: Implantation (human embryo)
Content:  In humans, implantation is the stage of human reproduction at which the embryo adheres to the wall of the uterus. At this stage of prenatal development, the conceptus is called a blastocyst. Once this adhesion is successful, the female is considered to be pregnant and the embryo will receive oxygen and nutrients from the mother in order to grow. In humans, implantation of a fertilized ovum is most likely to occur around nine days after ovulation; however, this can range between six and 12 days.
Title: Implantation (human embryo)
Content:  The reception-ready phase of the endometrium of the uterus is usually termed the "implantation window" and lasts about 4 days. The implantation window occurs around 6 days after the peak in luteinizing hormone levels. With some disparity between sources, it has been stated to occur from 7 days after ovulation until 9 days after ovulation, or days 6–10 postovulation. On average, it occurs during the 20th to the 23rd day after the last menstrual period. The implantation window is characterized by changes to the endometrium cells, which aid in the absorption of the uterine fluid. These changes are collectively known as the plasma membrane transformation and bring the blastocyst nearer to the endometrium and immobilize it. During this stage the blastocyst can still be eliminated by being flushed out of the uterus. Scientists have hypothesized that the hormones cause a swelling that fills the flattened out uterine cavity just prior to this stage, which may also help press the blastocyst against the endometrium. The implantation window may also be initiated by other preparations in the endometrium of the uterus, both structurally and in the composition of its secretions.
Title: Implantation (human embryo)
Content:  Implantation is initiated when the blastocyst comes into contact with the uterine wall.
Title: Implantation bleeding
Content:  Implantation bleeding is a small amount of vaginal bleeding that can occur in early pregnancy due to the fertilized egg attaching to the inside of the uterus. Implantation bleeding occurs between 7 to 14 days after fertilization. Implantation bleeding may be accompanied by symptoms such as cramping, nausea, breast tenderness, and headaches. Implantation bleeding can be distinguished from period bleeding by color, clotting, strength of flow, and length of flow. However, there is no support for the notion that implantation produces vaginal bleeding. Bleeding and spotting are common during the luteal phase of the menstrual cycle as well as during early pregnancy, and for reasons unrelated to implantation.
Title: Implantation (human embryo)
Content:  The embryoblast spends approximately 72 hours in the uterine cavity before implanting. In that time, it cannot receive nourishment directly from the blood of the mother, and must rely on secreted nutrients into the uterine cavity, e.g. iron and fat-soluble vitamins.
Title: Prenatal development
Content:  The embryo becomes embedded in the endometrium in a process called implantation. In most successful pregnancies, the embryo implants 8 to 10 days after ovulation. The embryo, the extra-embryonic membranes, and the placenta are collectively referred to as a conceptus, or the "products of conception". Rapid growth occurs and the embryo's main features begin to take form. This process is called differentiation, which produces the varied cell types (such as blood cells, kidney cells, and nerve cells). A spontaneous abortion, or miscarriage, in the first trimester of pregnancy is usually due to major genetic mistakes or abnormalities in the developing embryo. During this critical period (most of the first trimester), the developing embryo is also susceptible to toxic exposures, such as: 
Title: Proembryo
Content:  The word 'pre-embryo' sometimes is used in ethical contexts to refer a human conceptus at least between fertilization and implantation, and is known too as a proembryo although this is not term which has been adopted by the scientific community. A conceptus between fertilization and implantation is also frequently classified as an embryo. Even after implantation begins, a preembryo (and proembryo) may exist up until formation of the primitive streak. Implantation begins at about six days after fertilization, and lasts for about a week, during which time formation of the primitive streak occurs. Use of the terms preembryo and proembryo, in the context of human development, has 
Title: Pregnancy rate
Content:  Implantation rate is the percentage of embryos which successfully undergo implantation compared to the number of embryos transferred in a given period. In practice, it is generally calculated as the number of intrauterine gestational sacs observed by transvaginal ultrasonography divided by the number of transferred embryos. As an example, one center in the United States reported an implantation rate in IVF of 37% at a maternal age of less than 35 years, 30% at 35 to 37 years, 22% at 38 to 40 years, and 12% at 41 to 42 years. Successful implantation of the zygote into the uterus is most likely 8 to 10 days after conception. If the zygote has not implanted by day 10, implantation becomes increasingly unlikely in subsequent days.
Title: Menstrual cycle
Content:  fraternal twins. After release from the ovary, the egg is swept into the fallopian tube by the fimbria – a fringe of tissue at the end of each fallopian tube. After about a day, an unfertilized egg disintegrates or dissolves in the fallopian tube, and a fertilized egg reaches the uterus in three to five days. Fertilization usually takes place in the ampulla, the widest section of the fallopian tubes. A fertilized egg immediately starts the process of embryogenesis (development). The developing embryo takes about three days to reach the uterus, and another three days to implant into the endometrium. It has usually reached the blastocyst stage at the time of implantation: this is when pregnancy begins. The loss 
Title: Timeline of human prenatal development
Content: Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into the uterine lining. They will eventually form the placenta and embryonic membranes. The blastocyst is fully implanted day 7–12 of fertilization. ; Formation of the yolk sac. ; The embryonic cells flatten into a disk, two cells thick. ; If separation into identical twins occurs, 2/3 of the time it will happen between days 5 and 9. If it happens after day 9, there is a significant risk of the twins being conjoined. ; Primitive streak develops. (day 13 of fertilization). ; Primary stem villi appear. (day 13 of fertilization). Gestational age: 3 weeks and 0 days until 3 weeks and 6 days old. 22–28 days from last menstruation. Embryonic age: Week nr 2. 1 week old. 8–14 days from fertilization. 

Question: when does the implantation of the embryo occur?
Answer: around 9 days after ovulation.