When should I tell my boss?

Laura • 💍 01.18.2014 9.20.2017 | 8.26.2019 | 5.27.2023
Luckily I do not work on Mondays, and all my appointments so far are being scheduled for Mondays. But when should I tell my boss? I'm kind of scared because I am a 1099 contract employee and because well, he doesn't have kids. Should I wait until after my ultrasound appointment on Oct 17? Or should i tell him right away?? I'm 4wks 6days and I feel like I could wait a little longer before spilling the beans...