NST at 34 weeks

I had a 34 week growth scan today due to placenta previa (although it finally moved up!). The tech seemed to put a lot of focus on the umbilical cord section of the scan, and took several several strips of its pulse which never happened at my other 5 growth scans. My husband reads EKGs for work, and said there was a 1.5 to 2 second pause on one of the strips of pulse but it could have just been positional. However at the end of the ultrasound the tech said she had to go run something by the high risk doctor that reads all of the scans and came back with an order for a NST 2x a week for the remainder of my pregnancy. The only explanation given was that since I have a history of high blood pressure they wanted to monitor more closely. The thing is, is my blood pressure has been in the 120s / 70s for the entirety of my pregnancy. Any one else had this happen to them? I feel like I’m not being told the full story.