Week 1: your baby is the size of stardust

Look, you are not pregnant yet. In fact, you are most likely on your period. Your baby is a distant glimmer of stardust that will fall to Earth in approximately 40 weeks, all starting with a Big Bang.

Week 1 is counted from the first day of your last period, which is a delightfully unscientific way to start a countdown. There is no embryo here yet, only potential and a single egg getting ready for its close-up.

Almost every atom heavier than helium inside that future baby was forged in a star. The calcium in the bones, the iron in the blood, the oxygen in every breath: all of it was cooked in stellar cores and scattered across the galaxy long before Earth existed.

Meanwhile, inside you

Before your baby is the size of any animal, they are the size of nothing at all, and made of everything.