gender blood work accuracy

Dina β€’ Wife and mum 1 boy and 3 angel babies want to start trying asap πŸ˜“
Hi all just wanting to know if anyone has done the gender blood work and just how accurate they are? I'm about 7 weeks now and still have not done my first ultrasound which is scheduled for next week. Any advice would be much appreciated. πŸ˜€