The signs that you’re pregnant are probably still hard to notice, but your baby – still an embryo – is taking some big steps.
As the cells grow and divide, they link up to your blood supply through the endometrium to draw nutrients for energy. By this stage, the embryo contains almost 200 cells. In these early stages it is laying the building blocks for what will eventually become its brain, hair, skin, internal organs and skeleton.
To support and protect itself, the embryo will start to develop a placenta and an amniotic sac. These provide a source of nutrients and an oxygen supply to help keep your baby alive and growing, and they are absolutely critical for the duration of your pregnancy.
You might also start to have an inkling that you are pregnant due to the hormonal changes your body is going through, causing fatigue, nausea and mood swings. Around the end of the fourth week you may notice that your period hasn’t arrived and, if you haven’t been testing, this might give you the first hint that you’re pregnant.