When does placenta take over

[19annie86]

Just wondering when does the placenta take over roughly, and would symptoms start to reduce, I'm approx just over 9 weeks, and nausea reduced alot and boobs not as sore

@19annie86
They say it takes over from 9 to 12 weeks.

I had my scan at 10+3 and was told the yolk sac was tiny and baby was positioned on the placenta. Probably varies as above.