What is a Non Stress Test? A NST tracks your babies' movements and heart rates and your contractions. It can tell your doctor whether your babies are reactive to movement and/or contractions. A baby's heart rate should go up when they move.
I started getting NSTs around week 32. I had my first one after an ultrasound when the technician and doctor did not see one of the babies practice breathing, which is one of the things they started to look for at each ultrasound towards the end of my pregnancy. This didn't mean he wasn't practicing breathing, he just wasn't practicing at that moment.
A NST is painless and easy. I sat in a recliner at my Maternal Fetal Medicine office and had three monitors placed on my belly. One was placed on Baby A, one on Baby B, and one in the middle of my belly to measure contractions. I had a button to push every time I felt any movement. I was told it can take up to 30 minutes before the doctors or nurses are able to tell your babies are reactive to movement. My babies were very active ALL. THE. TIME. so the NSTs never took very long, maybe 15 minutes. After my initial NST, I had them once per week and then twice per week from 34 weeks on.
Here's a video from one of my NSTs. The monitor to the left is on Baby B, the other one is the contraction monitor, and you can't see the monitor on Baby A because she was so low!