Conception, by definition, references the fertilization of an egg by sperm. Because sperm can survive for up to five days after ejaculation, it can take anywhere from a couple hours to five days before an egg actually becomes fertilized. However, if fertilization is to occur, it must happen within 12-24 hours after ovulation, as the egg can only survive for so long in the fallopian tube. It can take a total of 7 to 14 days for implantation to occur following sexual intercourse.
The fertilized egg, also known as the blastocyst, eventually attaches itself to the uterine wall and begins to produce hCG (the Human Chorionic Gonadotropin hormone). That is why pregnancy tests are engineered to detect hCG, because this means fertilization and implantation has already occurred, and voila! There is officially a baby on board.
But before the fertilized egg attaches itself to the uterine wall, it must make the arduous journey from the fallopian tube to the uterus, which results in the ‘implantation’ of the egg. This journey can take anywhere from 7-10 days. As the egg travels, it also continues to grow in size as the cells within it divide and reproduce.When the egg arrives at the uterus for implantation, a tissue known as trophoblast develops around the egg. The trophoblast tissue is what causes the egg to attach itself to the uterus and pulls the egg into the endometrium. Trophoblast also enters the mother’s blood vessels and works to redirect her blood to the egg. Implantation bleeding can sometimes occur as a result of two processes: when the egg is pulled into the endometrium, or when some of the redirected blood leaks out while it travels to the fertilized egg. Both of these are completely normal.