There are multiple indicators of a possible pregnancy which can begin a few days after conception: a missed period, mood swings, appetite change, sensitivity to smells and tastes, nausea, vomiting, breast tenderness, backaches, frequent urination and fatigue.
Pregnancy tests check for a hormone called hCG (human Chorionic Gonadotropin). It is made by pregnancy cells and developing placental tissues. hCG will pass into a woman’s system and will be present in both blood and urine samples. This hormone first appears in your urine from 10-14 days after fertilization but the longer you wait for testing the more accurate it will be.
How did this happen?
When an egg left your ovary, it entered and traveled inside your Fallopian tube. On that journey it was penetrated by a sperm causing fertilization. Each parent contributed 23 chromosomes.
Sperm can survive inside the vagina and uterus for 3- 5 days. By the time the fertilized egg reached your uterus, it grew from a single cell into a compact cluster of cells (blastocyst). This cluster attached (conception) and burrowed itself into your uterine lining (menstruation is shedding of the uterine lining). From that point on, this early embryo continues to develop into a fetus/baby.