paternity testing

Angie • 18 year old first time mommy w a baby due, July 2017❤️
First time mom. Currently 7 weeks and 2 days. I have my first ultrasound appointment December 13. I'm wanting to take a paternity test but I'm so impatient. Would I be okay taking a paternity test while pregnant? Has anyone taking a test while pregnant? Or which test is recommended. I'm really scared of having a miscarriage.... Advice on this anyone please!