Slow Fetal Cardiac Activity at 5.5weeks

Hi I’m having an IVF pregnancy. Went for my first scan at what was supposed to be 6 weeks but there was only a gestational sac and yolk, no fetal pole. Went for second scan yesterday a week later and there was fetal pole and heartbeat detected. Embryo dated at 5.5weeks but heartbeat noted to be slow and recommended for a follow up scan. Anyone had the same experience? Would love to hear stories if their babies managed to catch up or that the pregnancies developed smoothly after. This is really quite agonising - like I’m happy that there’s a heartbeat now but also don’t dare to let myself be happy too in case it’s not viable. After the first visit I had already prepared myself for the worst so it’s really a rollercoaster of emotions.