The extra testosterone can increase body hair, but it falls out later.

Just like other skin surfaces on the body, the areola (dark circle around the nipple) contains hair follicles, so hair on the breast is considered normal. Shaving or plucking could lead to inflection, so if the hair is bothersome, it’s best to cut with a small scissors.
Many times, the condition is linked to high levels of male hormones (called androgens). It’s normal for women’s bodies to make these, and low levels don’t cause excess hair growth. But when these amounts are too high, they can cause hirsutism and other things, like acne, a deep voice, etc
You might find this an interesting read
https://www.webmd.com/women/guide/hirsutism-hair-women#1

It’s the influx of hormones. Usually your body will readjust but if concerned I suggest speaking to GP.

I have about 7 hairs on my boobs that I pluck since having my son – ah the joy!

no i had the lightest linea nigra though. no hair where it shouldn’t have been though. just those crazy preggo hormones hey

I didn’t but again everyone is different, if your worried ask your midwife or doctor about it

Body hair appears as you get older and it can also occur with hormone changes. Check with your GP if you think it is hormonal.