Is your boss expecting you to work as hard as your other employees? What do you do if you can't cope

I have told my boss that i am pregnant. However, recently he been increasing my workload same as other colleagues. He asked us to take out 6-7 projects on top of our daily work. As these projects are global, it will probably involved a lot of morning or night calls due to different time zone. I am worried if my body can take it. He seems to want me to work as hard as before with OTs etc. If i tell him i cant cope can he use this as underperformance to dismiss me? #pregnancy #advicepls #firstbaby