Implantation is the biological process during early pregnancy when a fertilized egg (embryo) attaches itself to the lining of the uterus (endometrium). This attachment marks the beginning of pregnancy. After fertilization occurs in the fallopian tube, the fertilized egg, now called a blastocyst, travels to the uterus and embeds into the uterine wall to receive nutrients and oxygen necessary for growth
. Implantation typically happens about 6 to 10 days after ovulation or fertilization. It involves several stages: the blastocyst hatches from its protective shell, adheres to the uterine lining, and then invades into the endometrium to establish a connection with the mother's blood supply, eventually leading to placenta formation
. This process requires the uterus to be receptive, which depends on complex molecular signaling between the embryo and the uterine lining. The "window of implantation" is a limited period when the uterus is prepared to accept the embryo, usually 5 to 10 days after ovulation
. Some women may experience mild symptoms during implantation, such as light bleeding (implantation bleeding), mild cramps, or changes in cervical mucus, but often implantation occurs without noticeable signs
. Successful implantation triggers the production of the hormone human chorionic gonadotropin (hCG), which is detected by pregnancy tests and confirms pregnancy
. In summary, implantation is the crucial early step in pregnancy where the fertilized egg embeds into the uterus to begin development, occurring roughly a week after fertilization
