The first week is all about putting in time, waiting for your period to end and the baby-making season to begin. One week pregnancy is actually not being pregnant at all. Most OBs count pregnancy starting from the first day of your last period. That’s because ovulation and conception are really tough to pinpoint, but the physical signs of menstruation are much easier to spot. So in doctor speak, 1 week pregnant means you’re on your period and not yet pregnant. You won’t actually conceive your baby until week two or three, depending on the length of your cycle.

Because pregnancy is dated based on the first day of the woman’s last menstrual period, the first day of your pregnancy is actually the first day of your last period. So this month startsout with your menstrual cycle.

Assuming you manage to conceive this month, your uterus will begin to undergo a rather remarkable metamorphosis that will see it increasing in capacity by up to 1,000 times over the course of your pregnancy. Its weight will increase dramatically at the same time: while your prepregnant uterus weighs approximately 2.5 ounces (70 grams), by the time you’re ready to give birth, your uterus will be a much heftier 21⁄2 pounds (1,100 grams).