Fetal tachycardia

Maggie • 29 years old, stay at home mom of a 5 yr old girl and 1 yr old girl. Tried getting pregnant for 5 months before trying out pre seed and got pregnant the first month. Due with #3 in August.
So, I am 35 weeks with my 3rd baby girl and for the past month she has had a high heart rate, which has caused me to have to go in for weekly non stress tests. Today she failed her NST and I had to get a biophysical profile done immediately after the test, which she passed very quickly. I am worried for my little girl. Is there anyone out there who has had their baby being monitored for fetal tachycardia and they were born with no complications or heart problems? Her highest HR has been around 180 bpm but more steady around 170s. I'm scheduled for a c section august 3rd, but if she continues to have issues I wonder if she'll be here sooner. Any advice would be helpful.. my Dr doesn't seem all too concerned. She just wants to keep monitoring her with NST's.