When should I call the doctor if I noticed there is no fetal movement after a few hours?

Concerned 2nd time mom at 9 months. I understand there is little room left for movement. But, I noticed this evening our baby has not moved since early evening. Or I was waay busy with what I was doing and missed his movement. It's now 2am and I have been monitoring for the last 2 hours or so. Nothing yet.
Concerned 2nd time mom at 9 months. I understand there is little room left for movement. But, I noticed this evening our baby has not moved since early evening. Or I was waay busy with what I was doing and missed his movement. It's now 2am and I have been monitoring for the last 2 hours or so. Nothing yet. **** Update Thank you all for your answers I am now drinking water with ice. I tried OJ earlier and thought that was sweet enough.