Is it official yet? Not quite—but be assured that your body's got those baby-making mechanics well under way. After fertilization, your ovaries start ramping up the production of progesterone, a hormone that prepares your uterus to host the newly fertilized egg, or zygote, that will live there for the next 38 weeks or so.
Right now, you're just dying to find out: Am I pregnant or not? Unfortunately, you'll need to stick it out a bit longer. About four days after your egg is fertilized, it begins producing a hormone called human chorionic gonadotropin (HCG), which pregnancy tests can detect in about another week—first in your blood (via a test at your doctor's office) and then in your urine (which an at-home screening would spot).